bonding: fix error return code in bond_enslave()

Fix to return a negative error code in the add bond vlan ids error
handling case instead of 0, as done elsewhere in this function.

Introduced by commit 1ff412ad.
(bonding: change the bond's vlan syncing functions with the standard ones)
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -1603,7 +1603,8 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 		dev_mc_add(slave_dev, lacpdu_multicast);
 	}
 
-	if (vlan_vids_add_by_dev(slave_dev, bond_dev)) {
+	res = vlan_vids_add_by_dev(slave_dev, bond_dev);
+	if (res) {
 		pr_err("%s: Error: Couldn't add bond vlan ids to %s\n",
 		       bond_dev->name, slave_dev->name);
 		goto err_close;