RDMA: Convert drivers to use the AH's sgid_attr in post_wr paths

For UD the drivers were doing a sgid_index lookup into the cache to get
the attrs, however we can now directly access the same attrs stores in
the ib_ah instead and remove the lookup.

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

drivers/infiniband/hw/mthca/mthca_av.c

@@ -281,10 +281,7 @@ int mthca_read_ah(struct mthca_dev *dev, struct mthca_ah *ah,
 		header->grh.flow_label    =
 			ah->av->sl_tclass_flowlabel & cpu_to_be32(0xfffff);
 		header->grh.hop_limit     = ah->av->hop_limit;
-		ib_get_cached_gid(&dev->ib_dev,
-				  be32_to_cpu(ah->av->port_pd) >> 24,
-				  ah->av->gid_index % dev->limits.gid_table_len,
-				  &header->grh.source_gid, NULL);
+		header->grh.source_gid = ah->ibah.sgid_attr->gid;
 		memcpy(header->grh.destination_gid.raw,
 		       ah->av->dgid, 16);
 	}