staging: gdm724x: constantify 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
wwan_type variable to be a constant structure as well, placing it into
read-only memory which can not be modified at runtime.
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Link: https://lore.kernel.org/r/20240217-device_cleanup-staging-v1-1-286479d9a3f0@marliere.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/gdm724x/gdm_lte.c

@@ -43,7 +43,7 @@ static struct {
 	struct sock *sock;
 } lte_event;
 
-static struct device_type wwan_type = {
+static const struct device_type wwan_type = {
 	.name   = "wwan",
 };