Latest drivers version requires phy-mode to be set. Otherwise we will
use "NA" mode and the switch driver will invalidate this port mode.

Fixes: 65ac79e1 ("net: dsa: microchip: add the phylink get_caps")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20220610081621.584393-1-o.rempel@pengutronix.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>