nvme-rdma: Use ibdev_to_node instead of dereferencing ->dma_device

->dma_device is a private implementation detail of the RDMA core.  Use the
ibdev_to_node helper to get the NUMA node for a ib_device instead of
poking into ->dma_device.

Link: https://lore.kernel.org/r/20201106181941.1878556-5-hch@lst.de


Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>