games/moonlight-embedded: unbreak with ffmpeg 4.0

src/video/ffmpeg.c:99:27: error: use of undeclared identifier 'CODEC_FLAG_LOW_DELAY'

decoder_ctx->flags |= CODEC_FLAG_LOW_DELAY;
                      ^

src/video/sdl.c:43:48: error: use of undeclared identifier 'FF_INPUT_BUFFER_PADDING_SIZE'

ffmpeg_buffer = malloc(DECODER_BUFFER_SIZE + FF_INPUT_BUFFER_PADDING_SIZE);
                                             ^

PR: 227726