implement finish

Change-Id: If1ec99d0dbcf7aebf9d90d7779bf3ff34a8963f2
diff --git a/rs_hal.h b/rs_hal.h
index 16bd890..9ae6fed 100644
--- a/rs_hal.h
+++ b/rs_hal.h
@@ -287,6 +287,7 @@
         void (*destroy)(const Context *rsc, const ScriptGroup *sg);
     } scriptgroup;
 
+    void (*finish)(const Context *rsc);
 } RsdHalFunctions;