net: dsa: mt7530: Fix traffic flooding for MMIO devices

On MMIO devices (e.g. MT7988 or EN7581) unicast traffic received on lanX
port is flooded on all other user ports if the DSA switch is configured
without VLAN support since PORT_MATRIX in PCR regs contains all user
ports. Similar to MDIO devices (e.g. MT7530 and MT7531) fix the issue
defining default VLAN-ID 0 for MT7530 MMIO devices.

Fixes: 110c18b ("net: dsa: mt7530: introduce driver for MT7988 built-in switch")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Chester A. Unal <chester.a.unal@arinc9.com>
Link: https://patch.msgid.link/20250304-mt7988-flooding-fix-v1-1-905523ae83e9@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: LorenzoBianconi

drivers/net/dsa/mt7530.c

@@ -2591,7 +2591,8 @@ mt7531_setup_common(struct dsa_switch *ds)
 	if (ret < 0)
 		return ret;
 
-	return 0;
+	/* Setup VLAN ID 0 for VLAN-unaware bridges */
+	return mt7530_setup_vlan0(priv);
 }
 
 static int
@@ -2687,11 +2688,6 @@ mt7531_setup(struct dsa_switch *ds)
 	if (ret)
 		return ret;
 
-	/* Setup VLAN ID 0 for VLAN-unaware bridges */
-	ret = mt7530_setup_vlan0(priv);
-	if (ret)
-		return ret;
-
 	ds->assisted_learning_on_cpu_port = true;
 	ds->mtu_enforcement_ingress = true;