nbd: restructure sock_shutdown

This patch restructures sock_shutdown to avoid having the main code path
in an if block.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/nbd.c

@@ -119,13 +119,14 @@ static void nbd_end_request(struct nbd_device *nbd, struct request *req)
  */
 static void sock_shutdown(struct nbd_device *nbd)
 {
-	if (nbd->sock) {
+	if (!nbd->sock)
+		return;
+
 	dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
 	kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
 	nbd->sock = NULL;
 	del_timer_sync(&nbd->timeout_timer);
 }
-}
 
 static void nbd_xmit_timeout(unsigned long arg)
 {