Add libpng include path

 Forward compatibility change

Change-Id: Iae792715d9a9aea34f53cd6383981371835c4a31
diff --git a/cmds/screenshot/screenshot.c b/cmds/screenshot/screenshot.c
index cca80c3..be1ecd4 100644
--- a/cmds/screenshot/screenshot.c
+++ b/cmds/screenshot/screenshot.c
@@ -8,7 +8,7 @@
 #include <linux/fb.h>
 
 #include <zlib.h>
-#include <libpng/png.h>
+#include <png.h>
 
 #include "private/android_filesystem_config.h"