media: v4l2-ctrls: Return the handler's error in v4l2_ctrl_handler_free()

v4l2_ctrl_handler_free() used to return void but changing this to int,
returning the handler's error code, enables the drivers to simply return
the handler's error in this common error handling pattern:

	if (handler->error)
		return v4l2_ctrl_handler_free(handler);

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>