net: mv643xx_eth: fix missing device_node for port devices

DT-based mv643xx_eth probes and creates platform_devices for the
port devices on its own. To allow fixups for ports based on the
device_node, we need to set .of_node of the corresponding device
with the correct node.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: David S. Miller <davem@davemloft.net>