We don't need to save the dma device as it's not used in the hot path
and hasn't in a long time. Shrink the struct nvme_queue removing this
unnecessary member.
Signed-off-by: NKeith Busch <keith.busch@intel.com>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>
Signed-off-by: NChristoph Hellwig <hch@lst.de>