Actually fix build breakage with cleanspec.

OUT_DIR instead of OUT

Test: manual
Change-Id: I2e48c6f2f39ff2318517ff55cbfa6ca912c05021
diff --git a/CleanSpec.mk b/CleanSpec.mk
index 11846f6..c557635 100644
--- a/CleanSpec.mk
+++ b/CleanSpec.mk
@@ -53,3 +53,4 @@
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/lib64/hw/android.hardware.bluetooth*)
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/etc/init/android.hardware.bluetooth*)
 $(call add-clean-step, rm -rf $(OUT)/soong/.intermediates/)
+$(call add-clean-step, rm -rf $(OUT_DIR)/soong/.intermediates/hardware/interfaces/)