filmstripenc: fix rounding that caused fate failure

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/filmstripenc.c

@@ -64,7 +64,7 @@ static int write_trailer(AVFormatContext *s)
     avio_wb16(pb, st->codec->width);
     avio_wb16(pb, st->codec->height);
     avio_wb16(pb, 0);  // leading
-    avio_wb16(pb, 1/av_q2d(st->codec->time_base));
+    avio_wb16(pb, st->codec->time_base.den / st->codec->time_base.num);
     for (i = 0; i < 16; i++)
         avio_w8(pb, 0x00);  // reserved