nvme-auth: don't use NVMe status codes

NVMe status codes are part of the wire protocol, and shouldn't be
fabricated in the stack. So with this patch the authentication code
is switched over to use error codes; as a side effect authentication
failures due to internal error won't be retried anymore.
But that shouldn't have happened anyway.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>