rds_rdma: don't assume infiniband device is PCI

RDS code assumes that the struct ib_device dma_device member, which is a
pointer, points to a struct device embedded in a struct pci_dev.

This is not the case for ehca, for example, which is a OF driver, and
makes dma_device point to a struct device embedded in a struct
platform_device.

This will make the system crash when rds_rdma is loaded in a system
with ehca, since it will try to access the bus member of a non-existent
struct pci_dev.

The only reason rds_rdma uses the struct pci_dev is to get the NUMA node
the device is attached to. Using dev_to_node for that is much better,
since it won't assume which bus the infiniband is attached to.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Cc: dledford@redhat.com
Cc: Jes.Sorensen@redhat.com
Cc: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Acked-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>