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.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>