fix build

Change-Id: Ic00efe260d579b761ea50217fe806c485052d7e1
diff --git a/products/cyanogen_vega.mk b/products/cyanogen_vega.mk
index c1e3efe..2579973 100644
--- a/products/cyanogen_vega.mk
+++ b/products/cyanogen_vega.mk
@@ -1,7 +1,7 @@
 $(call inherit-product, device/advent/vega/vega.mk)
 
 # skips themes and keeps the resulting rom tiny so it fits on /system/ with all languages included
-SKIP_THEMES := true
+PRODUCT_SPECIFIC_DEFINES += SKIP_THEMES=true
 
 # Inherit some common cyanogenmod stuff.
 $(call inherit-product, vendor/cyanogen/products/common_full.mk)