net: stmmac: Fix VLAN filtering when HW does not support it

If we don't have any filters available we can't rely upon the return
code of stmmac_add_hw_vlan_rx_fltr() / stmmac_del_hw_vlan_rx_fltr(). Add
a check for this.

Fixes: ed64639 ("net: stmmac: Add support for VLAN Rx filtering")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -4566,9 +4566,13 @@ static int stmmac_vlan_rx_add_vid(struct net_device *ndev, __be16 proto, u16 vid
 		return ret;
 	}
 
-	ret = stmmac_add_hw_vlan_rx_fltr(priv, ndev, priv->hw, proto, vid);
+	if (priv->hw->num_vlan) {
+		ret = stmmac_add_hw_vlan_rx_fltr(priv, ndev, priv->hw, proto, vid);
+		if (ret)
+			return ret;
+	}
 
-	return ret;
+	return 0;
 }
 
 static int stmmac_vlan_rx_kill_vid(struct net_device *ndev, __be16 proto, u16 vid)
@@ -4581,9 +4585,12 @@ static int stmmac_vlan_rx_kill_vid(struct net_device *ndev, __be16 proto, u16 vi
 		is_double = true;
 
 	clear_bit(vid, priv->active_vlans);
-	ret = stmmac_del_hw_vlan_rx_fltr(priv, ndev, priv->hw, proto, vid);
-	if (ret)
-		return ret;
+
+	if (priv->hw->num_vlan) {
+		ret = stmmac_del_hw_vlan_rx_fltr(priv, ndev, priv->hw, proto, vid);
+		if (ret)
+			return ret;
+	}
 
 	return stmmac_vlan_update(priv, is_double);
 }