We have to use := instead of +=

If we use +=, the right side may be deferred to evaluate,
if that target-specific variable is not defined yet.
That's a mistke.

Change-Id: I1635ee4791473f407866e010d612948c02cdebf6

core/base_rules.mk

@@ -434,7 +434,7 @@ endif
 ###########################################################
 cleantarget := clean-$(LOCAL_MODULE)
 $(cleantarget) : PRIVATE_MODULE := $(LOCAL_MODULE)
-$(cleantarget) : PRIVATE_CLEAN_FILES += \
+$(cleantarget) : PRIVATE_CLEAN_FILES := \
     $(LOCAL_BUILT_MODULE) \
     $(LOCAL_INSTALLED_MODULE) \
     $(intermediates)