net: mtk_eth_soc: stop passing phylink state to sgmii setup

Now that mtk_sgmii_setup_mode_force() only uses the interface mode
from the phylink state, pass just the interface mode into this
function.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>