Fix typo in build_rro_package.mk

S should be $

Bug: 36797383
Test: build sailfish
Change-Id: I06abfd76c6524368c318c965086cee6d029c4b48
diff --git a/core/build_rro_package.mk b/core/build_rro_package.mk
index 9865b33..ffefb9c 100644
--- a/core/build_rro_package.mk
+++ b/core/build_rro_package.mk
@@ -15,7 +15,7 @@
   $(error runtime resource overlay package should not contain sources)
 endif
 
-ifeq (S(LOCAL_RRO_THEME),)
+ifeq ($(LOCAL_RRO_THEME),)
   LOCAL_MODULE_PATH := $(TARGET_OUT_VENDOR)/overlay
 else
   LOCAL_MODULE_PATH := $(TARGET_OUT_VENDOR)/overlay/$(LOCAL_RRO_THEME)