net: phy: xgmiitorgmii: Use correct mdio bus

The xgmiitorgmii is using the mii_bus of the device it's attached to,
instead of the bus it was given during probe.

Signed-off-by: Brandon Maier <brandon.maier@rockwellcollins.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>