nvme-pci: rename nvme_disable_io_queues

This function really deletes the I/O queues, so rename it to match
the functionality.  Also move the main wrapper right next to the
actual underlying implementation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>