asfdec: fix build for big endian targets

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit aabc2682)

libavformat/asfdec.c

@@ -361,6 +361,7 @@ static int asf_read_stream_properties(AVFormatContext *s, int64_t size)
         /* This code assumes that extradata contains only palette */
         /* This is true for all paletted codecs implemented in ffmpeg */
         if (st->codec->extradata_size && (st->codec->bits_per_coded_sample <= 8)) {
+            int av_unused i;
             st->codec->palctrl = av_mallocz(sizeof(AVPaletteControl));
 #if HAVE_BIGENDIAN
             for (i = 0; i < FFMIN(st->codec->extradata_size, AVPALETTE_SIZE)/4; i++)