net: phy: marvell: Use the unlocked genphy_c45_ethtool_get_eee()

phy_ethtool_get_eee() is about to gain locking of the phydev lock.
This means it cannot be used within a PHY driver without causing a
deadlock. Swap to using genphy_c45_ethtool_get_eee() which assumes the
lock has already been taken.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>