HID: make hid_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the hid_bus_type variable to be a constant structure as well,
placing it into read-only memory which can not be modified at runtime.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

drivers/hid/hid-core.c

@@ -2749,7 +2749,7 @@ static int hid_uevent(const struct device *dev, struct kobj_uevent_env *env)
 	return 0;
 }
 
-struct bus_type hid_bus_type = {
+const struct bus_type hid_bus_type = {
 	.name		= "hid",
 	.dev_groups	= hid_dev_groups,
 	.drv_groups	= hid_drv_groups,

include/linux/hid.h

@@ -912,7 +912,7 @@ extern bool hid_ignore(struct hid_device *);
 extern int hid_add_device(struct hid_device *);
 extern void hid_destroy_device(struct hid_device *);
 
-extern struct bus_type hid_bus_type;
+extern const struct bus_type hid_bus_type;
 
 extern int __must_check __hid_register_driver(struct hid_driver *,
 		struct module *, const char *mod_name);