switchdev: make struct switchdev_attr parameter const for attr_set calls

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 43d7342..84cd863 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -453,7 +453,7 @@
 }
 
 static int dsa_slave_port_attr_set(struct net_device *dev,
-				   struct switchdev_attr *attr,
+				   const struct switchdev_attr *attr,
 				   struct switchdev_trans *trans)
 {
 	struct dsa_slave_priv *p = netdev_priv(dev);