nbd: share nbd_put and return by goto put_nbd

Replace the following two statements by the statement “goto put_nbd;”

	nbd_put(nbd);
	return 0;
Signed-off-by: Sun Ke <sunke32@huawei.com>
Suggested-by: Markus Elfring <Markus.Elfring@web.de>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20210512114331.1233964-3-sunke32@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -2015,12 +2015,11 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
 		return -EINVAL;
 	}
 	mutex_unlock(&nbd_index_mutex);
-	if (!refcount_inc_not_zero(&nbd->config_refs)) {
-		nbd_put(nbd);
-		return 0;
-	}
+	if (!refcount_inc_not_zero(&nbd->config_refs))
+		goto put_nbd;
 	nbd_disconnect_and_put(nbd);
 	nbd_config_put(nbd);
+put_nbd:
 	nbd_put(nbd);
 	return 0;
 }