libcamera: controls: Default ControlList validator argument to nullptr

The ControlList constructor takes a validator pointer that can be null.
Set its default value to nullptr to simplify code in users of
ControlList.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Tested-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/request.cpp

@@ -69,7 +69,7 @@ Request::Request(Camera *camera, uint64_t cookie)
 	/**
 	 * \todo: Add a validator for metadata controls.
 	 */
-	metadata_ = new ControlList(nullptr);
+	metadata_ = new ControlList();
 }
 
 Request::~Request()