vlc: fix build with newer freetype from oe-core

* ftsynth.h header was moved to freetype2 and vlc is broken since:
  commit 7cbf6060ac14b0f4d2f038f821ca980be0d46cb0
  Author: Ross Burton <ross.burton@intel.com>
  Date:   Mon Nov 11 17:25:22 2013 +0000
  Subject: freetype: upgrade to 2.5.0.1

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>