mmal/mmal_picture: Don't wait inifinitely for picture

Use mmal_queue_timedwait instead of mmal_queue_wait to avoid deadlocks if due
to some unexpected reason no mmal buffer is available for a picture to be
locked. This makes the mmal plugins more robust against mmal internal
failures.
Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/hw/mmal/mmal_picture.c

@@ -40,7 +40,7 @@ int mmal_picture_lock(picture_t *picture)
 
     vlc_mutex_lock(get_mmal_opaque_mutex());
 
-    MMAL_BUFFER_HEADER_T *buffer = mmal_queue_wait(pic_sys->queue);
+    MMAL_BUFFER_HEADER_T *buffer = mmal_queue_timedwait(pic_sys->queue, 2);
     if (!buffer) {
         ret = VLC_EGENERIC;
         goto out;