nvmet-auth: fix return value check in auth receive

nvmet_auth_challenge() return type is int and currently it uses status
variable that is of type u16 in nvmet_execute_auth_receive().

Catch the return value of nvmet_auth_challenge() into int and set the
NVME_SC_INTERNAL as status variable before we jump to error.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>