net: phy: Uniform PHY driver access

struct phy_device contains a pointer to the PHY driver and nearly
everywhere this pointer is used to access the PHY driver. Only
mdio_bus_phy_may_suspend() is still using to_phy_driver() instead of the
PHY driver pointer. Uniform PHY driver access by eliminating
to_phy_driver() use in mdio_bus_phy_may_suspend().

Only phy_bus_match() and phy_probe() are still using to_phy_driver(),
because PHY driver pointer is not available there.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>