libcamera: camera: Add a const version of the pipe() function

Allow access to the pipeline handler on a const instance of
Camera::Private.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

include/libcamera/internal/camera.h

@@ -32,6 +32,7 @@ public:
 	~Private();
 
 	PipelineHandler *pipe() { return pipe_.get(); }
+	const PipelineHandler *pipe() const { return pipe_.get(); }
 
 	std::list<Request *> queuedRequests_;
 	ControlInfoMap controlInfo_;