subsys/bluetooth: Add missing stdint.h include

This tiny header uses non-builtin types but includes no headers that
would define them.  Recent header motion seems to have exposed a case
where this file can get built before its dependencies are included.
Add the header directly.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>

subsys/bluetooth/controller/hal/cntr.h

@@ -4,6 +4,7 @@
  *
  * SPDX-License-Identifier: Apache-2.0
  */
+#include <stdint.h>
 
 void cntr_init(void);
 uint32_t cntr_start(void);