[media] uvcvideo: Allow userptr IO mode

Userptr can be very useful if a UVC camera is requested to use video
buffers allocated by another processing device. So that buffers don't
need to be copied.

Signed-off-by: Javier Martin <[e-mail]>
Acked-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/video/uvc/uvc_queue.c

···
 		    int drop_corrupted)
 {
 	queue->queue.type = type;
-	queue->queue.io_modes = VB2_MMAP;
+	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
 	queue->queue.drv_priv = queue;
 	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
 	queue->queue.ops = &uvc_queue_qops;