avfilter: make avfilter_default_free_video_buffer() static

This function is not referenced outside this file and has no
prototype.  Feel free to flame if this is wrong.

Originally committed as revision 22314 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/defaults.c

@@ -23,7 +23,7 @@
 #include "avfilter.h"
 
 /* TODO: buffer pool.  see comment for avfilter_default_get_video_buffer() */
-void avfilter_default_free_video_buffer(AVFilterPic *pic)
+static void avfilter_default_free_video_buffer(AVFilterPic *pic)
 {
     av_free(pic->data[0]);
     av_free(pic);