net: phy: genphy_c45_pma_baset1_setup_master_slave: do no set unknown configuration

Do not change default master/slave forced configuration if no changes was
requested.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>