net: dsa: retain a per-port device_node pointer

We will later use the per-port device_node pointer to fetch a bunch of
port-specific properties.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index ad1a913..5688c34 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -354,6 +354,7 @@
 	}
 
 	SET_NETDEV_DEV(slave_dev, parent);
+	slave_dev->dev.of_node = ds->pd->port_dn[port];
 	slave_dev->vlan_features = master->vlan_features;
 
 	p = netdev_priv(slave_dev);