mediacontrol: Fix warnings about unused args.

src/control/mediacontrol_audio_video.c

@@ -55,6 +55,7 @@ mediacontrol_snapshot( mediacontrol_Instance *self,
                        const mediacontrol_Position * a_position,
                        mediacontrol_Exception *exception )
 {
+    (void)a_position;
     vlc_object_t* p_cache;
     vout_thread_t* p_vout;
     input_thread_t *p_input;

src/control/mediacontrol_core.c

@@ -330,6 +330,7 @@ mediacontrol_get_stream_information( mediacontrol_Instance *self,
                                      mediacontrol_PositionKey a_key,
                                      mediacontrol_Exception *exception )
 {
+    (void)a_key;
     mediacontrol_StreamInformation *retval = NULL;
     libvlc_media_t * p_media;
     libvlc_exception_t ex;