libcamera: rkisp1: Do not over-write metadata

When a Request is completed upon receiving the IPA produced metadata,
the metadata associated with the Request are over-written, deleting
the information set at output buffer completion, such as the
SensorTimestamp.

This commit applies to the RkISP1 pipeline handler the same change
applied to IPU3 in commit 2ee3dd57e2fc ("libcamera: ipu3: Merge IPA
metadata controls").

Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/pipeline/rkisp1/rkisp1.cpp

@@ -365,7 +365,7 @@ void RkISP1CameraData::metadataReady(unsigned int frame, const ControlList &meta
 	if (!info)
 		return;
 
-	info->request->metadata() = metadata;
+	info->request->metadata().merge(metadata);
 	info->metadataProcessed = true;
 
 	pipe->tryCompleteRequest(info->request);