nvmet-auth: remove some dead code

'status' is known to be 0 at the point.
And nvmet_auth_challenge() return a -E<ERROR_CODE> or 0.
So these lines of code should just be removed.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>