nvme-auth: auth success1 msg always includes resp

In cases where RVALID is false, the response is still transmitted,
but is cleared to zero.

Relevant extract from the spec:
Response R2, if valid (i.e., if the RVALID field is set to 01h),
cleared to 0h otherwise

Signed-off-by: Mark O'Donovan <shiftee@posteo.net>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>