Fix various warnings: static /void / comma

src/sensor/SDL_sensor.c

@@ -149,7 +149,7 @@ SDL_SensorID *SDL_GetSensors(int *count)
  * Return the next available sensor instance ID
  * This may be called by drivers from multiple threads, unprotected by any locks
  */
-SDL_SensorID SDL_GetNextSensorInstanceID()
+SDL_SensorID SDL_GetNextSensorInstanceID(void)
 {
     return SDL_AtomicIncRef(&SDL_last_sensor_instance_id) + 1;
 }