net: phy: fix null dereference in phy_attach_direct

Commit bc66fa87 ("net: phy: Add link between phy dev and mac dev")
introduced a link between net devices and phy devices. It fails to check
whether dev is NULL, leading to a NULL dereference error.

Fixes: bc66fa87 ("net: phy: Add link between phy dev and mac dev")
Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy_device.c

@@ -1517,7 +1517,7 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	 * another mac interface, so we should create a device link between
 	 * phy dev and mac dev.
 	 */
-	if (phydev->mdio.bus->parent && dev->dev.parent != phydev->mdio.bus->parent)
+	if (dev && phydev->mdio.bus->parent && dev->dev.parent != phydev->mdio.bus->parent)
 		phydev->devlink = device_link_add(dev->dev.parent, &phydev->mdio.dev,
 						  DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);