static int unimac_mdio_remove(struct platform_device *pdev)
{
	struct unimac_mdio_priv *priv = platform_get_drvdata(pdev);

	mdiobus_unregister(priv->mii_bus);
	mdiobus_free(priv->mii_bus);

	return 0;
}

The product dereferences a pointer that it expects to be valid but is NULL.