avcodec/rkmppdec: Fix double-free on error

After having created the AVBuffer that is put into frame->buf[0],
ownership of several objects (namely an AVDRMFrameDescriptor,
an MppFrame and some AVBufferRefs framecontextref and decoder_ref)
has passed to the AVBuffer and therefore to the frame.
Yet it has nevertheless been freed manually on error
afterwards, which would lead to a double-free as soon
as the AVFrame is unreferenced.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/rkmppdec.c

@@ -463,8 +463,8 @@ static int rkmpp_retrieve_frame(AVCodecContext *avctx, AVFrame *frame)
 
             frame->hw_frames_ctx = av_buffer_ref(decoder->frames_ref);
             if (!frame->hw_frames_ctx) {
-                ret = AVERROR(ENOMEM);
-                goto fail;
+                av_frame_unref(frame);
+                return AVERROR(ENOMEM);
             }
 
             return 0;