net: phy: Add missing driver check in phy_aneg_done()

Dan's static checker caught a potential code path in phy_state_machine() where
we were not checking phydev->drv which is in phy_aneg_done().

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 25149ef9

 ("net: phy: Check phydev->drv")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>