mlx5: Replace PCI pool old API

The PCI pool API is deprecated. This commit replaces the PCI pool old
API by the appropriate function with the DMA pool API.

Signed-off-by: Romain Perier <romain.perier@collabora.com>
Reviewed-by: Peter Senna Tschudin <peter.senna@collabora.com>
Acked-by: Doug Ledford <dledford@redhat.com>
Tested-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>