IB/mthca: Use correct GID in MADs sent on port 2

mthca_create_ah() includes the port number in the GID index. The reverse
needs to be done in mthca_read_ah().

Noted by Hal Rosenstock.
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_av.c

@@ -184,7 +184,7 @@ int mthca_read_ah(struct mthca_dev *dev, struct mthca_ah *ah,
 			ah->av->sl_tclass_flowlabel & cpu_to_be32(0xfffff);
 		ib_get_cached_gid(&dev->ib_dev,
 				  be32_to_cpu(ah->av->port_pd) >> 24,
-				  ah->av->gid_index,
+				  ah->av->gid_index % dev->limits.gid_table_len,
 				  &header->grh.source_gid);
 		memcpy(header->grh.destination_gid.raw,
 		       ah->av->dgid, 16);