Mark gsize variable as av_unused, fixes the warning:

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


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@18620 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

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);