libcamera: framebuffer: Make FrameBuffer::cancel() private

FrameBuffer::cancel() is not meant to be used by applications. Move it
to the FrameBuffer::Private class.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@puri.sm>
[Kieran: Handle rebase]
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/framebuffer.h

@@ -31,6 +31,8 @@ public:
 	Fence *fence() const { return fence_.get(); }
 	void setFence(std::unique_ptr<Fence> fence) { fence_ = std::move(fence); }
 
+	void cancel() { LIBCAMERA_O_PTR()->metadata_.status = FrameMetadata::FrameCancelled; }
+
 private:
 	std::unique_ptr<Fence> fence_;
 	Request *request_;