remove useless cast

Originally committed as revision 24553 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dvdsubdec.c

@@ -460,7 +460,7 @@ static int dvdsub_decode(AVCodecContext *avctx,
 {
     const uint8_t *buf = avpkt->data;
     int buf_size = avpkt->size;
-    AVSubtitle *sub = (void *)data;
+    AVSubtitle *sub = data;
     int is_menu;
 
     is_menu = decode_dvd_subtitles(sub, buf, buf_size);