net: dsa: use dsa_to_port helper everywhere

Do not let the drivers access the ds->ports static array directly
while there is a dsa_to_port helper for this purpose.

At the same time, un-const this helper since the SJA1105 driver
assigns the priv member of the returned dsa_port structure.

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
diff --git a/net/dsa/switch.c b/net/dsa/switch.c
index 6a96075..df4abe8 100644
--- a/net/dsa/switch.c
+++ b/net/dsa/switch.c
@@ -20,7 +20,7 @@ static unsigned int dsa_switch_fastest_ageing_time(struct dsa_switch *ds,
 	int i;
 
 	for (i = 0; i < ds->num_ports; ++i) {
-		struct dsa_port *dp = &ds->ports[i];
+		struct dsa_port *dp = dsa_to_port(ds, i);
 
 		if (dp->ageing_time && dp->ageing_time < ageing_time)
 			ageing_time = dp->ageing_time;
@@ -98,7 +98,7 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
 	if (unset_vlan_filtering) {
 		struct switchdev_trans trans = {0};
 
-		err = dsa_port_vlan_filtering(&ds->ports[info->port],
+		err = dsa_port_vlan_filtering(dsa_to_port(ds, info->port),
 					      false, &trans);
 		if (err && err != EOPNOTSUPP)
 			return err;