adpcm: Fix a comment in the trellis heap code

This makes the wording consistent with how people usually talk about heaps.

Originally committed as revision 25775 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/adpcm.c

@@ -420,7 +420,7 @@ static void adpcm_compress_trellis(AVCodecContext *avctx, const short *samples,
                     u->sample1 = dec_sample;\
                     paths[u->path].nibble = nibble;\
                     paths[u->path].prev = nodes[j]->path;\
-                    /* Sift the newly inserted node down in the heap to \
+                    /* Sift the newly inserted node up in the heap to \
                      * restore the heap property. */\
                     while (pos > 0) {\
                         int parent = (pos - 1) >> 1;\