Fixing a missing header compilation problem

samples/c/facedetect.cpp

@@ -3,6 +3,7 @@
 #include <opencv2/imgproc/imgproc.hpp>
 
 #include <iostream>
+#include <stdio.h>
 
 using namespace std;
 using namespace cv;
@@ -204,4 +205,4 @@ void detectAndDraw( Mat& img,
         }
     }  
     cv::imshow( "result", img );    
-}
\ No newline at end of file
+}