build: Use TOPDIR, not TOP

Change-Id: I5b2677c22aa878e46e01f4e5b31769e21937c38a
diff --git a/build/core/config.mk b/build/core/config.mk
index 963fef4..5f46cab 100644
--- a/build/core/config.mk
+++ b/build/core/config.mk
@@ -1,5 +1,5 @@
 # Copyright (C) 2015 The CyanogenMod Project
-#           (C) 2017 The LineageOS Project
+#           (C) 2017-2018 The LineageOS Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -20,4 +20,4 @@
 FRAMEWORK_LINEAGE_PLATFORM_REMOVED_API_FILE := $(TOPDIR)lineage-sdk/api/lineage_removed.txt
 FRAMEWORK_LINEAGE_API_NEEDS_UPDATE_TEXT := $(TOPDIR)vendor/lineage/build/core/apicheck_msg_current.txt
 
-BUILD_RRO_SYSTEM_PACKAGE := $(TOP)/vendor/lineage/build/core/system_rro.mk
+BUILD_RRO_SYSTEM_PACKAGE := $(TOPDIR)vendor/lineage/build/core/system_rro.mk