[media] uvcvideo: Don't fail when an unsupported format is requested

Return the default format in that case.
This issue was found by the v4l2-compliance tool.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/usb/uvc/uvcvideo.h

@@ -436,6 +436,7 @@ struct uvc_streaming {
 	struct uvc_format *format;
 
 	struct uvc_streaming_control ctrl;
+	struct uvc_format *def_format;
 	struct uvc_format *cur_format;
 	struct uvc_frame *cur_frame;
 	/* Protect access to ctrl, cur_format, cur_frame and hardware video