net: dsa: update DSA drivers to use ds_to_priv

Use the helper function to retrieve the driver private context instead of
using (void *)(ds + 1).

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dsa/mv88e6131.c b/drivers/net/dsa/mv88e6131.c
index dadfafb..953bc6a 100644
--- a/drivers/net/dsa/mv88e6131.c
+++ b/drivers/net/dsa/mv88e6131.c
@@ -155,7 +155,7 @@
 
 static int mv88e6131_setup_port(struct dsa_switch *ds, int p)
 {
-	struct mv88e6xxx_priv_state *ps = (void *)(ds + 1);
+	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
 	int addr = REG_PORT(p);
 	u16 val;
 
@@ -274,7 +274,7 @@
 
 static int mv88e6131_setup(struct dsa_switch *ds)
 {
-	struct mv88e6xxx_priv_state *ps = (void *)(ds + 1);
+	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
 	int i;
 	int ret;