libcamera: converter: Utilise shared MediaDevice pointers

With the upcoming addition of V4L2 requests support, the converters need
to keep a handle to the corresponding media device.

Prepare for that by changing the constructor parameter from a raw
pointer to a shared pointer.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>

src/libcamera/pipeline/simple/simple.cpp

@@ -415,7 +415,7 @@ public:
 
 	V4L2VideoDevice *video(const MediaEntity *entity);
 	V4L2Subdevice *subdev(const MediaEntity *entity);
-	MediaDevice *converter() { return converter_.get(); }
+	std::shared_ptr<MediaDevice> converter() { return converter_; }
 	bool swIspEnabled() const { return swIspEnabled_; }
 
 protected:
@@ -588,7 +588,7 @@ int SimpleCameraData::init()
 	int ret;
 
 	/* Open the converter, if any. */
-	MediaDevice *converter = pipe->converter();
+	std::shared_ptr<MediaDevice> converter = pipe->converter();
 	if (converter) {
 		converter_ = ConverterFactoryBase::create(converter);
 		if (!converter_) {