avs: don't set codec timebase

Demuxers are not supposed to set it.
Set r_frame_rate and avg_frame_rate instead.

libavformat/avs.c

@@ -188,8 +188,8 @@ static int avs_read_packet(AVFormatContext * s, AVPacket * pkt)
                     avs->st_video->codec->height = avs->height;
                     avs->st_video->codec->bits_per_coded_sample=avs->bits_per_sample;
                     avs->st_video->nb_frames = avs->nb_frames;
-                    avs->st_video->codec->time_base = (AVRational) {
-                    1, avs->fps};
+                    avs->st_video->r_frame_rate = avs->st_video->avg_frame_rate =
+                                                  (AVRational){avs->fps, 1};
                 }
                 return avs_read_video_packet(s, pkt, type, sub_type, size,
                                              palette, palette_size);