net: dsa: destroy the phylink instance on any error in dsa_slave_phy_setup

DSA supports connecting to a phy-handle, and has a fallback to a non-OF
based method of connecting to an internal PHY on the switch's own MDIO
bus, if no phy-handle and no fixed-link nodes were present.

The -ENODEV error code from the first attempt (phylink_of_phy_connect)
is what triggers the second attempt (phylink_connect_phy).

However, when the first attempt returns a different error code than
-ENODEV, this results in an unbalance of calls to phylink_create and
phylink_destroy by the time we exit the function. The phylink instance
has leaked.

There are many other error codes that can be returned by
phylink_of_phy_connect. For example, phylink_validate returns -EINVAL.
So this is a practical issue too.

Fixes: aab9c4067d ("net: dsa: Plug in PHYLINK support")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20210914134331.2303380-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/slave.c

@@ -1854,13 +1854,11 @@ static int dsa_slave_phy_setup(struct net_device *slave_dev)
 		 * use the switch internal MDIO bus instead
 		 */
 		ret = dsa_slave_phy_connect(slave_dev, dp->index, phy_flags);
-		if (ret) {
-			netdev_err(slave_dev,
-				   "failed to connect to port %d: %d\n",
-				   dp->index, ret);
-			phylink_destroy(dp->pl);
-			return ret;
-		}
+	}
+	if (ret) {
+		netdev_err(slave_dev, "failed to connect to PHY: %pe\n",
+			   ERR_PTR(ret));
+		phylink_destroy(dp->pl);
 	}
 
 	return ret;