nvme: rename _nvme_revalidate_disk

Rename _nvme_revalidate_disk to nvme_validate_ns to better describe
what the function does, and pass the struct nvme_ns instead of the
gendisk to better match the call chain.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>