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/phy/at803x.c b/drivers/net/phy/at803x.c
index 62361f8..b76ac09 100644
--- a/drivers/net/phy/at803x.c
+++ b/drivers/net/phy/at803x.c
@@ -190,7 +190,7 @@
 
 static int at803x_probe(struct phy_device *phydev)
 {
-	struct device *dev = &phydev->dev;
+	struct device *dev = &phydev->mdio.dev;
 	struct at803x_priv *priv;
 	struct gpio_desc *gpiod_reset;