add #include so make checkheaders passes

Originally committed as revision 23637 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/vsrc_buffer.h

@@ -19,6 +19,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "avfilter.h"
+
 int av_vsrc_buffer_add_frame(AVFilterContext *buffer_filter, AVFrame *frame,
                              int64_t pts, AVRational pixel_aspect);