net: dsa: use port's cpu_dp when creating a slave

When dsa_slave_create is called, the related port already has a CPU port
assigned to it, available in its cpu_dp member. Use it instead of the
unique tree cpu_dp.
Signed-off-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dsa/slave.c

@@ -1117,16 +1117,13 @@ int dsa_slave_resume(struct net_device *slave_dev)
 int dsa_slave_create(struct dsa_port *port, const char *name)
 {
 	struct dsa_notifier_register_info rinfo = { };
+	struct dsa_port *cpu_dp = port->cpu_dp;
+	struct net_device *master = cpu_dp->netdev;
 	struct dsa_switch *ds = port->ds;
-	struct net_device *master;
 	struct net_device *slave_dev;
 	struct dsa_slave_priv *p;
-	struct dsa_port *cpu_dp;
 	int ret;
 
-	cpu_dp = ds->dst->cpu_dp;
-	master = cpu_dp->netdev;
-
 	if (!ds->num_tx_queues)
 		ds->num_tx_queues = 1;