[media] v4l2-ctrls: Correctly destroy mutex in v4l2_ctrl_handler_free()

The mutex that was initialised in v4l2_ctrl_handler_init_class() was not
destroyed in v4l2_ctrl_handler_free(). Do that.

Additionally, explicitly refer to the ctrl handler's mutex in mutex
initialisation for clarity.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/v4l2-core/v4l2-ctrls.c

@@ -1739,8 +1739,8 @@ int v4l2_ctrl_handler_init_class(struct v4l2_ctrl_handler *hdl,
 				 unsigned nr_of_controls_hint,
 				 struct lock_class_key *key, const char *name)
 {
+	mutex_init(&hdl->_lock);
 	hdl->lock = &hdl->_lock;
-	mutex_init(hdl->lock);
 	lockdep_set_class_and_name(hdl->lock, key, name);
 	INIT_LIST_HEAD(&hdl->ctrls);
 	INIT_LIST_HEAD(&hdl->ctrl_refs);
@@ -1780,6 +1780,7 @@ void v4l2_ctrl_handler_free(struct v4l2_ctrl_handler *hdl)
 	hdl->cached = NULL;
 	hdl->error = 0;
 	mutex_unlock(hdl->lock);
+	mutex_destroy(&hdl->_lock);
 }
 EXPORT_SYMBOL(v4l2_ctrl_handler_free);