nvme: cleanup __nvme_check_ids

Pass the actual nvme_ns_ids used for the comparison instead of the
ns_head that isn't needed and use a more descriptive function name.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>