Fix broken comment on closing #endif in window.h

The closing #endif comment is missing the comment delimiters. This
change adds them and fixes a compile warning about extra tokens after
endif.

Change-Id: If8295aa6fbb2b21c2b56fe57a467dcde79c65de3
diff --git a/include/system/window.h b/include/system/window.h
index 4b0381b..5762a50 100644
--- a/include/system/window.h
+++ b/include/system/window.h
@@ -454,4 +454,4 @@
 
 __END_DECLS
 
-#endif SYSTEM_CORE_INCLUDE_ANDROID_WINDOW_H
+#endif /* SYSTEM_CORE_INCLUDE_ANDROID_WINDOW_H */