phy: Add an mdio_device structure

Not all devices attached to an MDIO bus are phys. So add an
mdio_device structure to represent the generic parts of an mdio
device, and place this structure into the phy_device.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 15b1f6b..fabc8df 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -3714,7 +3714,7 @@
 
 		mvneta_fixed_link_update(pp, phy);
 
-		put_device(&phy->dev);
+		put_device(&phy->mdio.dev);
 	}
 
 	return 0;