net/mlx4: replace pci_{,un}map_sg with dma_{,un}map_sg

pci_{,un}map_sg are deprecated and replaced by dma_{,un}map_sg. This is
especially relevant since the rest of the driver uses the DMA API. Fix
the driver to use the replacement APIs.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>