net: phy: use phy_resolve_aneg_linkmode in genphy_read_status

Now that we have phy_resolve_aneg_linkmode() we can make
genphy_read_status() much simpler.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>