[media] gspca: remove needless check before usb_free_coherent()

usb_free_coherent() is safe with NULL addr and this check is
not required.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/usb/gspca/gspca.c

@@ -567,7 +567,6 @@ static void destroy_urbs(struct gspca_dev *gspca_dev)
 
 		gspca_dev->urb[i] = NULL;
 		usb_kill_urb(urb);
-		if (urb->transfer_buffer != NULL)
 		usb_free_coherent(gspca_dev->dev,
 				  urb->transfer_buffer_length,
 				  urb->transfer_buffer,