net: fec: fix regression in link change accounting

A link-down isn't properly saved in the FEC state, so we wouldn't restart the
FEC after a repeated link-up.

Regression was introduced with commit
d97e7497 "net: fec: restart the FEC when PHY speed changes"

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>