nbd: fix incorrect unlock of nbd->sock_lock in sock_shutdown

Commit 0eadf37afc250 ("nbd: allow block mq to deal with timeouts")
changed normal usage of nbd->sock_lock to use spin_lock/spin_unlock
rather than the *_irq variants, but it missed this unlock in an
error path.

Found by Coverity, CID 1373871.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Markus Pargmann <mpa@pengutronix.de>
Fixes: 0eadf37afc250 ("nbd: allow block mq to deal with timeouts")
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/nbd.c

@@ -164,7 +164,7 @@ static void sock_shutdown(struct nbd_device *nbd)
 	spin_lock(&nbd->sock_lock);
 
 	if (!nbd->sock) {
-		spin_unlock_irq(&nbd->sock_lock);
+		spin_unlock(&nbd->sock_lock);
 		return;
 	}