init: make sepolicy dependency optional

Test: make system/core/init
Change-Id: Ie2e7ba57fe885baf017ef12334aea7f2f9f8f0c1
diff --git a/init/Android.mk b/init/Android.mk
index c63760c..39af0e6 100644
--- a/init/Android.mk
+++ b/init/Android.mk
@@ -2,7 +2,7 @@
 
 LOCAL_PATH:= $(call my-dir)
 
-include system/sepolicy/policy_version.mk
+-include system/sepolicy/policy_version.mk
 
 # --