phy: Consistently use addr for address on an MII bus

Within phy.h, an address on an MII bus has been called both addr and
phy_id. phy_id is particularly confusion, since it also means the ID
found in register 3, if the device on the bus is a phy. Consistently
use addr.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>