nvme-pci: refactor nvme_disable_io_queues

Pass the opcode for the delete SQ/CQ command as an argument instead of
the somewhat confusing pass loop.

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