avcodec/utils: unbreak BINKAUDIO_DCT duration calculation

libavcodec/utils.c

@@ -1668,14 +1668,10 @@ static int get_audio_frame_duration(enum AVCodecID id, int sr, int ch, int ba,
             return 256 * sr / 245;
         else if (id == AV_CODEC_ID_DST)
             return 588 * sr / 44100;
-
-        if (ch > 0) {
-            /* calc from sample rate and channels */
-            if (id == AV_CODEC_ID_BINKAUDIO_DCT) {
-                if (sr / 22050 > 22)
-                    return 0;
-                return (480 << (sr / 22050)) / ch;
-            }
+        else if (id == AV_CODEC_ID_BINKAUDIO_DCT) {
+            if (sr / 22050 > 22)
+                return 0;
+            return (480 << (sr / 22050));
         }
 
         if (id == AV_CODEC_ID_MP3)