Rename video-specific variables in recorder

This paves the way to add audio-specific variables.

PR #3757 <https://github.com/Genymobile/scrcpy/pull/3757>

app/src/scrcpy.c

@@ -435,7 +435,7 @@ scrcpy(struct scrcpy_options *options) {
         }
         recorder_started = true;
 
-        sc_demuxer_add_sink(&s->video_demuxer, &s->recorder.packet_sink);
+        sc_demuxer_add_sink(&s->video_demuxer, &s->recorder.video_packet_sink);
     }
 
     struct sc_controller *controller = NULL;