RDMA/mlx5: Use PCI device for dma mappings

DMA operation of the IB device is done using ib_device->dma_device.

Instead of accessing parent of the IB device, use the PCI dma device which
is setup to ib_device->dma_device during IB device registration.

Link: https://lore.kernel.org/r/20201125064628.8431-1-leon@kernel.org


Signed-off-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>