net: ethernet: fix kernel OOPS when remove davinci_mdio module

davinci mdio device is not unregistered from mdiobus when removing
the module, which causes BUG_ON() when free the device from mdiobus.

Calling mdiobus_unregister() before mdiobus_free() fixes the issue.
Signed-off-by: NBin Liu <b-liu@ti.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/davinci_mdio.c

@@ -394,8 +394,10 @@ static int __devexit davinci_mdio_remove(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct davinci_mdio_data *data = dev_get_drvdata(dev);
 
-	if (data->bus)
+	if (data->bus) {
+		mdiobus_unregister(data->bus);
 		mdiobus_free(data->bus);
+	}
 
 	if (data->clk)
 		clk_put(data->clk);