Mark gsize variable as av_unused, fixes the warning:

libavformat/asfdec.c:995: warning: unused variable ‘gsize’

Originally committed as revision 18620 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/asfdec.c

@@ -992,7 +992,7 @@ static void asf_build_simple_index(AVFormatContext *s, int stream_index)
     if (!guidcmp(&g, &index_guid)) {
         int64_t itime;
         int pct, ict;
-        int64_t gsize= get_le64(s->pb);
+        int64_t av_unused gsize= get_le64(s->pb);
         get_guid(s->pb, &g);
         itime=get_le64(s->pb);
         pct=get_le32(s->pb);