lavc/v4l2_context: Change the type of the ioctl cmd to uint32_t.

Fixes a warning on recent Linux:
libavcodec/v4l2_context.c: In function 'ff_v4l2_context_set_status':
libavcodec/v4l2_context.c:496:26: warning: comparison is always false due to limited range of data type

libavcodec/v4l2_context.c

@@ -484,7 +484,7 @@ static int v4l2_get_coded_format(V4L2Context* ctx, uint32_t *p)
   *
   *****************************************************************************/
 
-int ff_v4l2_context_set_status(V4L2Context* ctx, int cmd)
+int ff_v4l2_context_set_status(V4L2Context* ctx, uint32_t cmd)
 {
     int type = ctx->type;
     int ret;

libavcodec/v4l2_context.h

@@ -135,7 +135,7 @@ void ff_v4l2_context_release(V4L2Context* ctx);
  *                those frames will be dropped.
  * @return 0 in case of success, a negative value representing the error otherwise.
  */
-int ff_v4l2_context_set_status(V4L2Context* ctx, int cmd);
+int ff_v4l2_context_set_status(V4L2Context* ctx, uint32_t cmd);
 
 /**
  * Dequeues a buffer from a V4L2Context to an AVPacket.