Bluetooth: constify the struct device_type usage

Since commit aed65af ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the bt_type and
bnep_type variables to be constant structures 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>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/6lowpan.c

@@ -572,7 +572,7 @@ static void netdev_setup(struct net_device *dev)
 	dev->needs_free_netdev	= true;
 }
 
-static struct device_type bt_type = {
+static const struct device_type bt_type = {
 	.name	= "bluetooth",
 };
 

net/bluetooth/bnep/core.c

@@ -549,7 +549,7 @@ static struct device *bnep_get_device(struct bnep_session *session)
 	return &conn->hcon->dev;
 }
 
-static struct device_type bnep_type = {
+static const struct device_type bnep_type = {
 	.name	= "bluetooth",
 };