net/fec: no need to check for validity of ndev in suspend and resume

dev_set_drvdata is called unconditionally in the probe function and so
it cannot be NULL.

Reported-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>