net: dsa: lantiq_gswip: fix use-after-free on failed probe

Make sure to disable and deregister the switch on late probe errors to
avoid use-after-free when the device-resource-managed switch is freed.

Fixes: 14fceff4 ("net: dsa: Add Lantiq / Intel DSA driver for vrx200")
Cc: stable <stable@vger.kernel.org>	# 4.20
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/lantiq_gswip.c

@@ -1099,7 +1099,7 @@ static int gswip_probe(struct platform_device *pdev)
 		dev_err(dev, "wrong CPU port defined, HW only supports port: %i",
 			priv->hw_info->cpu_port);
 		err = -EINVAL;
-		goto mdio_bus;
+		goto disable_switch;
 	}
 
 	platform_set_drvdata(pdev, priv);
@@ -1109,6 +1109,9 @@ static int gswip_probe(struct platform_device *pdev)
 		 (version & GSWIP_VERSION_MOD_MASK) >> GSWIP_VERSION_MOD_SHIFT);
 	return 0;
 
+disable_switch:
+	gswip_mdio_mask(priv, GSWIP_MDIO_GLOB_ENABLE, 0, GSWIP_MDIO_GLOB);
+	dsa_unregister_switch(priv->ds);
 mdio_bus:
 	if (mdio_np)
 		mdiobus_unregister(priv->ds->slave_mii_bus);