usb: remove @return doc for void functions

For functions returning nothing, there is no need to document
with @return, as Doxgen complains about "documented empty
return type of ...".

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

include/usb/usb_device.h

@@ -404,8 +404,6 @@ int usb_transfer_sync(uint8_t ep, uint8_t *data, size_t dlen, unsigned int flags
  *
  * @param[in]  ep           Endpoint address corresponding to the one
  *                          listed in the device configuration table
- *
- * @return 0 on success, negative errno code on fail.
  */
 void usb_cancel_transfer(uint8_t ep);
 

samples/subsys/usb/webusb/src/webusb.c

@@ -127,8 +127,6 @@ int webusb_vendor_handle_req(struct usb_setup_packet *pSetup,
  * for handling the device requests.
  *
  * @param [in] handlers Pointer to WebUSB request handlers structure
- *
- * @return N/A
  */
 void webusb_register_request_handlers(struct webusb_req_handlers *handlers)
 {
@@ -161,8 +159,6 @@ done:
  * @brief Callback used to know the USB connection status
  *
  * @param status USB device status code.
- *
- * @return  N/A.
  */
 static void webusb_dev_status_cb(struct usb_cfg_data *cfg,
 				 enum usb_dc_status_code status,

samples/subsys/usb/webusb/src/webusb.h

@@ -35,8 +35,6 @@ struct webusb_req_handlers {
  * for handling requests.
  *
  * @param [in] handlers Pointer to WebUSB request handlers structure
- *
- * @return N/A
  */
 void webusb_register_request_handlers(struct webusb_req_handlers *handlers);
 

subsys/usb/class/cdc_acm.c

@@ -299,8 +299,6 @@ done:
  *
  * @param ep        Endpoint address.
  * @param ep_status Endpoint status code.
- *
- * @return  N/A.
  */
 static void cdc_acm_int_in(uint8_t ep, enum usb_dc_ep_cb_status_code ep_status)
 {
@@ -442,8 +440,6 @@ static void cdc_interface_config(struct usb_desc_header *head,
  * IRQ.
  *
  * @param work Address of work item.
- *
- * @return N/A.
  */
 static void cdc_acm_irq_callback_work_handler(struct k_work *work)
 {
@@ -549,8 +545,6 @@ static int cdc_acm_fifo_read(const struct device *dev, uint8_t *rx_data,
  * @brief Enable TX interrupt
  *
  * @param dev CDC ACM device struct.
- *
- * @return N/A.
  */
 static void cdc_acm_irq_tx_enable(const struct device *dev)
 {
@@ -567,8 +561,6 @@ static void cdc_acm_irq_tx_enable(const struct device *dev)
  * @brief Disable TX interrupt
  *
  * @param dev CDC ACM device struct.
- *
- * @return N/A.
  */
 static void cdc_acm_irq_tx_disable(const struct device *dev)
 {
@@ -599,8 +591,6 @@ static int cdc_acm_irq_tx_ready(const struct device *dev)
  * @brief Enable RX interrupt
  *
  * @param dev CDC ACM device struct.
- *
- * @return N/A
  */
 static void cdc_acm_irq_rx_enable(const struct device *dev)
 {
@@ -617,8 +607,6 @@ static void cdc_acm_irq_rx_enable(const struct device *dev)
  * @brief Disable RX interrupt
  *
  * @param dev CDC ACM device struct.
- *
- * @return N/A.
  */
 static void cdc_acm_irq_rx_disable(const struct device *dev)
 {
@@ -684,8 +672,6 @@ static int cdc_acm_irq_update(const struct device *dev)
  *
  * @param dev CDC ACM device struct.
  * @param cb  Callback function pointer.
- *
- * @return N/A
  */
 static void cdc_acm_irq_callback_set(const struct device *dev,
 				     uart_irq_callback_user_data_t cb,
@@ -722,8 +708,6 @@ int cdc_acm_dte_rate_callback_set(const struct device *dev,
  *
  * @param dev             CDC ACM device struct.
  * @param baudrate        Baud rate.
- *
- * @return N/A.
  */
 static void cdc_acm_baudrate_set(const struct device *dev, uint32_t baudrate)
 {
@@ -741,7 +725,8 @@ static void cdc_acm_baudrate_set(const struct device *dev, uint32_t baudrate)
  * @param dev CDC ACM device struct.
  * @param ep_status Endpoint status code.
  *
- * @return  N/A.
+ * @retval 0 on success.
+ * @retval -EIO if timed out.
  */
 static int cdc_acm_send_notification(const struct device *dev,
 				     uint16_t serial_state)

subsys/usb/usb_device.c

@@ -232,8 +232,6 @@ static bool usb_handle_request(struct usb_setup_packet *setup,
 
 /*
  * @brief send next chunk of data (possibly 0 bytes) to host
- *
- * @return N/A
  */
 static void usb_data_to_host(void)
 {
@@ -274,8 +272,6 @@ static void usb_data_to_host(void)
  *
  * @param [in] ep        Endpoint address
  * @param [in] ep_status Endpoint status
- *
- * @return N/A
  */
 static void usb_handle_control_transfer(uint8_t ep,
 					enum usb_dc_ep_cb_status_code ep_status)
@@ -398,8 +394,6 @@ static void usb_handle_control_transfer(uint8_t ep,
  *
  * @param [in] type       Type of request, e.g. USB_REQTYPE_TYPE_STANDARD
  * @param [in] handler    Callback function pointer
- *
- * @return N/A
  */
 static void usb_register_request_handler(int32_t type,
 					 usb_request_handler handler)