Fix v4l2 sink

The codec id to write as codec parameters is the one from the v4l2
encoder, not from the decoder.

Regression introduced by be985b8242.

Fixes #3795 <https://github.com/Genymobile/scrcpy/issues/3795>

app/src/v4l2_sink.c

@@ -210,6 +210,9 @@ sc_v4l2_sink_open(struct sc_v4l2_sink *vs, const AVCodecContext *ctx) {
         goto error_avformat_free_context;
     }
 
+    // The codec is from the v4l2 encoder, not from the decoder
+    ostream->codecpar->codec_id = encoder->id;
+
     int ret = avio_open(&vs->format_ctx->pb, vs->device_name, AVIO_FLAG_WRITE);
     if (ret < 0) {
         LOGE("Failed to open output device: %s", vs->device_name);