Headers for libvpx are installed into vpx subdirectory.

Originally committed as revision 23307 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/libvpxdec.c

@@ -24,8 +24,8 @@
  */
 
 #define VPX_CODEC_DISABLE_COMPAT 1
-#include <vpx_decoder.h>
-#include <vp8dx.h>
+#include <vpx/vpx_decoder.h>
+#include <vpx/vp8dx.h>
 
 #include "avcodec.h"