net: dsa: lantiq_gswip: ignore SerDes modes in phylink_mac_config()

net: dsa: lantiq_gswip: ignore SerDes modes in phylink_mac_config()

We can safely ignore SerDes interface modes 1000Base-X, 2500Base-X and
SGMII in phylink_mac_config() as they are being taken care of by the PCS
and the SGMII port anyway doesn't have MII_CFG and MII_PCDU registers
and hence gswip_phylink_mac_config() is already a no-op apart from
outputing a misleading error message.

Return early in case of SerDes interface modes to avoid printing that
error message.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Hauke Mehrtens <hauke@hauke-m.de>
Link: https://patch.msgid.link/dcb066d6a02e6340314b5ff4f73937757a4f8eb3.1756520811.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>