net: dsa: mv88e6xxx: Fix opps when adding vlan bridge

A port is not necessarily assigned to a netdev. And a port does not
need to be a member of a bridge. So when iterating over all ports,
check before using the netdev and bridge_dev for a port. Otherwise we
dereference a NULL pointer.

Fixes: da9c359e ("net: dsa: mv88e6xxx: check hardware VLAN in use")
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Reviewed-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -1775,6 +1775,9 @@ static int mv88e6xxx_port_check_hw_vlan(struct dsa_switch *ds, int port,
 			if (dsa_is_dsa_port(ds, i) || dsa_is_cpu_port(ds, i))
 				continue;
 
+			if (!ds->ports[port].netdev)
+				continue;
+
 			if (vlan.data[i] ==
 			    GLOBAL_VTU_DATA_MEMBER_TAG_NON_MEMBER)
 				continue;
@@ -1783,6 +1786,9 @@ static int mv88e6xxx_port_check_hw_vlan(struct dsa_switch *ds, int port,
 			    chip->ports[port].bridge_dev)
 				break; /* same bridge, check next VLAN */
 
+			if (!chip->ports[i].bridge_dev)
+				continue;
+
 			netdev_warn(ds->ports[port].netdev,
 				    "hardware VLAN %d already used by %s\n",
 				    vlan.vid,