fallout of cleaning-up libutils includes

Test: run & compile
Bug: n/a

Change-Id: I99e462d2db6560742fa3f065d5de50cd60111130
diff --git a/libs/ui/GraphicBuffer.cpp b/libs/ui/GraphicBuffer.cpp
index c4d8f76..9006178 100644
--- a/libs/ui/GraphicBuffer.cpp
+++ b/libs/ui/GraphicBuffer.cpp
@@ -16,6 +16,8 @@
 
 #define LOG_TAG "GraphicBuffer"
 
+#include <cutils/atomic.h>
+
 #include <ui/GraphicBuffer.h>
 
 #include <cutils/atomic.h>