nvme-pci: remove queue_count_ops for write_queues and poll_queues

queue_count_set() seems like that it has been provided to limit the
number of queue entries for write/poll queues.  But, the
queue_count_set() has been doing nothing but a parameter check even it
has num_possible_cpus() which is nop.

This patch removes entire queue_count_ops from the write_queues and
poll_queues.

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>