net: phy: fix autoneg mismatch case in genphy_read_status

The original patch didn't consider the case that autoneg process
finishes successfully but both link partners have no mode in common.
In this case there's no link, nevertheless we may be interested in
what the link partner advertised.

Like phydev->link we set phydev->autoneg_complete in
genphy_update_link() and use the stored value in genphy_read_status().
This way we don't have to read register BMSR again.

Fixes: b6163f19 ("net: phy: improve genphy_read_status")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>