Fixed bug 4277 - warnings patch

Sylvain

Patch a few warnings when using:
-Wmissing-prototypes -Wdocumentation -Wdocumentation-unknown-command

They are automatically enabled with -Wall

src/sensor/SDL_sensor.c

@@ -48,7 +48,7 @@ static SDL_bool SDL_updating_sensor = SDL_FALSE;
 static SDL_mutex *SDL_sensor_lock = NULL; /* This needs to support recursive locks */
 static SDL_atomic_t SDL_next_sensor_instance_id;
 
-void
+static void
 SDL_LockSensors(void)
 {
     if (SDL_sensor_lock) {
@@ -56,7 +56,7 @@ SDL_LockSensors(void)
     }
 }
 
-void
+static void
 SDL_UnlockSensors(void)
 {
     if (SDL_sensor_lock) {
@@ -118,7 +118,7 @@ SDL_SensorID SDL_GetNextSensorInstanceID()
  * Get the driver and device index for an API device index
  * This should be called while the sensor lock is held, to prevent another thread from updating the list
  */
-SDL_bool
+static SDL_bool
 SDL_GetDriverAndSensorIndex(int device_index, SDL_SensorDriver **driver, int *driver_index)
 {
     int i, num_sensors, total_sensors = 0;