nvme: split __nvme_revalidate_disk

Split out the code that applies the calculate value to a given disk/queue
into new helper that can be reused by the multipath code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>