net: macb: add of_phy_deregister_fixed_link to error paths

We add the call of_phy_deregister_fixed_link to all associated
error paths for memory clean up.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>