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>

include/net/dsa.h

@@ -41,6 +41,7 @@ struct dsa_chip_data {
 	 * or any other string to indicate this is a physical port.
 	 */
 	char		*port_names[DSA_MAX_PORTS];
+	struct device_node *port_dn[DSA_MAX_PORTS];
 
 	/*
 	 * An array (with nr_chips elements) of which element [a]