Add missing headers to get 'make checkheaders' closer to passing.

Originally committed as revision 15932 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/qcelpdata.h

@@ -29,7 +29,9 @@
  * @remark FFmpeg merging spearheaded by Kenan Gillet
  */
 
+#include <stddef.h>
 #include <stdint.h>
+#include "libavutil/common.h"
 
 /**
  * pre-calculated table for hammsinc function