net/fec: don't munge MAC address from platform data

When the MAC address is supplied via platform_data it should be OK as
it is and should not be modified in case of a dual FEC setup.
Also copying the MAC from platform_data to the single 'macaddr'
variable will overwrite the MAC for the first interface in case of a
dual FEC setup.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>