media: stk1160: Restore deleted comment in stk1160_fill_urb()

This comment explains why we return success when usb_alloc_noncoherent()
fails and I think it's helpful. It was deleted during a recent refactor,
but let's add it back.

Signed-off-by: Dan Carpenter <[e-mail]>
Reviewed-by: Xu Yang <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/usb/stk1160/stk1160-video.c

···
 	stk_urb->transfer_buffer = usb_alloc_noncoherent(dev->udev, sb_size,
 							 GFP_KERNEL, &stk_urb->dma,
 							 DMA_FROM_DEVICE, &stk_urb->sgt);
-	if (!stk_urb->transfer_buffer)
+	if (!stk_urb->transfer_buffer) {
+		/*
+		 * If the buffer allocation failed, we exit but return 0 since
+		 * we allow the driver working with less buffers.
+		 */
 		goto free_urb;
+	}
 
 	stk_urb->dev = dev;
 	return 0;