usb: gadget: function: uvc: conditionally dequeue

We shouldn't try to dequeue a NULL pointer.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/function/uvc_video.c

@@ -352,7 +352,8 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
 
 	if (!enable) {
 		for (i = 0; i < UVC_NUM_REQUESTS; ++i)
-			usb_ep_dequeue(video->ep, video->req[i]);
+			if (video->req[i])
+				usb_ep_dequeue(video->ep, video->req[i]);
 
 		uvc_video_free_requests(video);
 		uvcg_queue_enable(&video->queue, 0);