net: phy: improve genphy_read_status

This patch improves few aspects of genphy_read_status():

- Don't initialize lpagb, it's not needed.

- Move initializing phydev->speed et al before the if clause.

- In auto-neg case, skip populating lp_advertising if we
  don't have a link. This avoids quite some unnecessary
  MDIO reads in case of phylib polling mode.

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