IB/mthca: Rename to_ib_ah_attr to to_rdma_ah_attr

local function  to_ib_ah_attr is renamed so it in
sync with the rename of the ib_ah_attr structure

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Don Hiatt <don.hiatt@intel.com>
Reviewed-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>