lavf/matroskaenc: use integers to for display size.

Avoid rounding differences between x86_32 and x86_64.
Fix trac ticket #1997.

libavformat/matroskaenc.c

@@ -637,7 +637,7 @@ static int mkv_write_tracks(AVFormatContext *s)
                 }
 
                 if (st->sample_aspect_ratio.num) {
-                    int d_width = codec->width*av_q2d(st->sample_aspect_ratio);
+                    int d_width = av_rescale(codec->width, st->sample_aspect_ratio.num, st->sample_aspect_ratio.den);
                     put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYWIDTH , d_width);
                     put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYHEIGHT, codec->height);
                 }