Add Android.mk as a dependency as well

Change-Id: I19e91eb766fcc55e9a610421a67a7c8706fdaa46
diff --git a/keystore-engine/Android.mk b/keystore-engine/Android.mk
index acad442..40fb6c3 100644
--- a/keystore-engine/Android.mk
+++ b/keystore-engine/Android.mk
@@ -37,4 +37,6 @@
 	libbinder \
 	libkeystore_binder
 
+LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/Android.mk
+
 include $(BUILD_SHARED_LIBRARY)