Address a few compiler warnings

Change-Id: I6e063fba8d58c8c53da6bca6292c84e3392aee50
diff --git a/minuitwrp/graphics_utils.c b/minuitwrp/graphics_utils.c
index 96f6449..6083c75 100644
--- a/minuitwrp/graphics_utils.c
+++ b/minuitwrp/graphics_utils.c
@@ -15,6 +15,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <png.h>
 #include <pixelflinger/pixelflinger.h>
 #include <linux/fb.h>