fixing mp3 detection patch by (John Ryland <jryland at trolltech dot com>)

Originally committed as revision 1213 to svn://svn.ffmpeg.org/ffmpeg/trunk

libav/raw.c

@@ -169,7 +169,7 @@ static int mpegvideo_probe(AVProbeData *p)
             if (code == SEQ_START_CODE ||
                 code == GOP_START_CODE ||
                 code == PICTURE_START_CODE)
-                return AVPROBE_SCORE_MAX - 1;
+                return 50 - 1;
             else
                 return 0;
         }