net: dsa: constify the struct device_type usage

Since commit aed65af1 ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the dsa_type
variable to be a constant structure as well, placing it into read-only
memory which can not be modified at runtime.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/user.c

@@ -2429,7 +2429,7 @@ static const struct net_device_ops dsa_user_netdev_ops = {
 	.ndo_fill_forward_path	= dsa_user_fill_forward_path,
 };
 
-static struct device_type dsa_type = {
+static const struct device_type dsa_type = {
 	.name	= "dsa",
 };