Makefile: Fix the location for payload signing key.

CL in [1] put it in a wrong path.

[1] commit 38812d684b73b4e2bbd2a4277fd9b0d8b3c7a810

Bug: 25715402
Change-Id: I01a105888844011eee083d5f4d694223599fa067
diff --git a/core/Makefile b/core/Makefile
index a183444..f64dc28 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -700,8 +700,8 @@
 # format.
 ifeq ($(AB_OTA_UPDATER),true)
 ifeq ($(BRILLO),)
-ALL_DEFAULT_INSTALLED_MODULES += $(TARGET_OUT_ETC)/security/update_engine/update-payload-key.pub.pem
-$(TARGET_OUT_ETC)/security/update_engine/update-payload-key.pub.pem: $(addsuffix .x509.pem,$(DEFAULT_KEY_CERT_PAIR))
+ALL_DEFAULT_INSTALLED_MODULES += $(TARGET_OUT_ETC)/update_engine/update-payload-key.pub.pem
+$(TARGET_OUT_ETC)/update_engine/update-payload-key.pub.pem: $(addsuffix .x509.pem,$(DEFAULT_KEY_CERT_PAIR))
 	$(hide) rm -f $@
 	$(hide) mkdir -p $(dir $@)
 	$(hide) openssl x509 -pubkey -noout -in $< > $@