sdk: Fix broken google_sdk and google_sdk_x86 add-on build.

This patch fixes the broken builds for PRODUCT-google_sdk-sdk_addon
and PRODUCT-google_sdk_x86-sdk_addon.

Change-Id: Iba0f23a03c143cd38aaba98b0bd0d52686330ed6
diff --git a/core/tasks/sdk-addon.mk b/core/tasks/sdk-addon.mk
index 2641a31..a617e43 100644
--- a/core/tasks/sdk-addon.mk
+++ b/core/tasks/sdk-addon.mk
@@ -58,7 +58,7 @@
         $(BUILT_SYSTEMIMAGE):images/$(TARGET_CPU_ABI)/system.img \
         $(BUILT_USERDATAIMAGE_TARGET):images/$(TARGET_CPU_ABI)/userdata.img \
         $(BUILT_RAMDISK_TARGET):images/$(TARGET_CPU_ABI)/ramdisk.img \
-        $(ANDROID_PRODUCT_OUT)/system/build.prop:images/$(TARGET_CPU_ABI)/build.prop \
+        $(PRODUCT_OUT)/system/build.prop:images/$(TARGET_CPU_ABI)/build.prop \
         $(target_notice_file_txt):images/$(TARGET_CPU_ABI)/NOTICE.txt
 
 # Generate rules to copy the requested files