fec: call fec_restart() in fec_open()

We called fec_stop() in fec_enet_close(), thus we have to call
fec_restart() in fec_enet_open().

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>