opencv_example: add missing #include statements

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/video_filter/opencv_example.cpp

@@ -41,6 +41,8 @@
 
 #include <opencv2/core/core_c.h>
 #include <opencv2/core/core.hpp>
+#include <opencv2/imgproc/imgproc_c.h>
+#include <opencv2/imgproc/imgproc.hpp>
 #include <opencv2/objdetect/objdetect.hpp>
 
 /*****************************************************************************