nvme: include admin_q sync with nvme_sync_queues

nvme_sync_queues currently syncs all namespace queues, but should
also sync the admin queue, if present.

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