net: phy: marvell10g: Let genphy_c45_pma_read_abilities set Aneg bit

The genphy_c45_pma_read_abilities helper now sets the Autoneg ability
in phydev->supported according to what the AN MMD reports.

We therefore don't need to manually do that in mv3310_get_features().

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Suggested-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>