nvme: improve the NVME_CONNECT_AUTHREQ* definitions

Mark them as unsigned so that we don't need extra casts, and define
them relative to cdword0 instead of requiring extra shifts.

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