ksz884x: fix return value of netdev_set_eeprom

netdev_set_eeprom() confused ethtool by just returning 1 on error
instead of a proper -EINVAL.
Signed-off-by: Jens Rottmann <JRottmann@LiPPERTEmbedded.de>
Signed-off-by: David S. Miller <davem@davemloft.net>