libcamera: camera_manager: Return a copy of the vector from cameras()

Making CameraManager::cameras() thread-safe requires returning a copy of
the cameras vector instead of a reference. This is also required for
hot-plugging support and is thus desirable.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/camera_manager.cpp

@@ -244,7 +244,7 @@ void CameraManager::stop()
  *
  * \return List of all available cameras
  */
-const std::vector<std::shared_ptr<Camera>> &CameraManager::cameras() const
+std::vector<std::shared_ptr<Camera>> CameraManager::cameras() const
 {
 	return p_->cameras_;
 }