asf: do not call av_read_frame

The asf_read_pts should read the bitstream directly.

libavformat/asfdec.c

@@ -1168,7 +1168,7 @@ static int64_t asf_read_pts(AVFormatContext *s, int stream_index, int64_t *ppos,
 //printf("asf_read_pts\n");
     asf_reset_header(s);
     for(;;){
-        if (av_read_frame(s, pkt) < 0){
+        if (asf_read_packet(s, pkt) < 0){
             av_log(s, AV_LOG_INFO, "asf_read_pts failed\n");
             return AV_NOPTS_VALUE;
         }