net: fec: make sure to init MAC address

Though we made sure to acquire a valid MAC for
the netdevice we never actually programmed it
into the hardware.
So if the bootloader did not set the MAC,
network operation would only work if userspace
explicitly asked to transfer the MAC to hardware.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>