net: dsa: Unregister slave_dev in error path

With commit 0071f56e46da ("dsa: Register netdev before phy"), we are now trying
to free a network device that has been previously registered, and in case of
errors, this will make us hit the BUG_ON(dev->reg_state != NETREG_UNREGISTERED)
condition.

Fix this by adding a missing unregister_netdev() before free_netdev().

Fixes: 0071f56e46da ("dsa: Register netdev before phy")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/slave.c

@@ -1204,6 +1204,7 @@ int dsa_slave_create(struct dsa_switch *ds, struct device *parent,
 	ret = dsa_slave_phy_setup(p, slave_dev);
 	if (ret) {
 		netdev_err(master, "error %d setting up slave phy\n", ret);
+		unregister_netdev(slave_dev);
 		free_netdev(slave_dev);
 		return ret;
 	}