blkdev_get_by_path() returns an ERR_PTR() or error and it doesn't return
a NULL.  It looks like this bug would be easy to trigger by mistake.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NNicholas A. Bellinger <nab@linux-iscsi.org>
Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>