apps: misc void main -> int main fixes

Fix some additional cases in in-tree applications (samples and tests).

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

samples/bluetooth/encrypted_advertising/central/src/main.c

@@ -103,16 +103,18 @@ static int setup_btn(void)
 	return 0;
 }
 
-void main(void)
+int main(void)
 {
 	int err;
 
 	err = setup_btn();
 	if (err) {
-		return;
+		return 0;
 	}
 
 	LOG_DBG("Starting central sample...");
 
 	(void)run_central_sample(get_passkey_confirmation, NULL, 0, NULL);
+
+	return 0;
 }

samples/bluetooth/encrypted_advertising/peripheral/src/main.c

@@ -97,16 +97,17 @@ static int setup_btn(void)
 	return 0;
 }
 
-void main(void)
+int main(void)
 {
 	int err;
 
 	err = setup_btn();
 	if (err) {
-		return;
+		return 0;
 	}
 
 	LOG_DBG("Starting peripheral sample...");
 
 	(void)run_peripheral_sample(get_passkey_confirmation);
+	return 0;
 }

samples/shields/npm1300_ek/src/main.c

@@ -37,13 +37,13 @@ void configure_ui(void)
 	printk("Set up button at %s pin %d\n", button1.port->name, button1.pin);
 }
 
-void main(void)
+int main(void)
 {
 	configure_ui();
 
 	if (!device_is_ready(regulators)) {
 		printk("Error: Regulator device is not ready\n");
-		return;
+		return 0;
 	}
 
 	while (1) {

tests/bsim/bluetooth/host/adv/encrypted/ead_sample/src/main.c

@@ -149,7 +149,8 @@ struct bst_test_list *test_ead_sample_install(struct bst_test_list *tests)
 
 bst_test_install_t test_installers[] = {test_ead_sample_install, NULL};
 
-void main(void)
+int main(void)
 {
 	bst_main();
+	return 0;
 }

tests/drivers/build_all/i2c/src/main.c

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-void main(void)
+int main(void)
 {
+	return 0;
 }