libcamera: pipeline_handler: Add const version of cameraData()

Add a version of cameraData() that returns a const pointer and mark it
as a const operation. The assert in the non-const version of the
function already enforces that a std::map::at() operation would always
succeed so there is no change in operation from the non-const version.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/pipeline_handler.h

@@ -97,6 +97,7 @@ protected:
 	virtual int queueRequestDevice(Camera *camera, Request *request) = 0;
 
 	CameraData *cameraData(const Camera *camera);
+	const CameraData *cameraData(const Camera *camera) const;
 
 	CameraManager *manager_;