Secretkeeper: require SECRETKEEPER_ENABLED=true

Make the makefile safer by requiring a specific value for the
environment variable that turns on Secretkeeper

Bug: 306364873
Test: TreeHugger
Change-Id: Ic5bb5e7411a19941f58ec8c973104c1e53f3834f
diff --git a/trusty/trusty-base.mk b/trusty/trusty-base.mk
index d645c3e..5aa4392 100644
--- a/trusty/trusty-base.mk
+++ b/trusty/trusty-base.mk
@@ -36,10 +36,10 @@
 endif
 
 # TODO(b/306364873): move this to be flag-controlled?
-ifeq ($(SECRETKEEPER_ENABLED),)
-    LOCAL_SECRETKEEPER_PRODUCT_PACKAGE :=
-else
+ifeq ($(SECRETKEEPER_ENABLED),true)
     LOCAL_SECRETKEEPER_PRODUCT_PACKAGE := android.hardware.security.secretkeeper.trusty
+else
+    LOCAL_SECRETKEEPER_PRODUCT_PACKAGE :=
 endif
 
 PRODUCT_PACKAGES += \