Module: Mark getters as const

Test: bluetooth_test_gd
Change-Id: Ieea21b113154bac1539a1ff73f4ca46ad37dfe35
diff --git a/gd/module.h b/gd/module.h
index 96a1109..0055d92 100644
--- a/gd/module.h
+++ b/gd/module.h
@@ -77,9 +77,9 @@
   // Release all resources, you're about to be deleted
   virtual void Stop() = 0;
 
-  ::bluetooth::os::Handler* GetHandler();
+  ::bluetooth::os::Handler* GetHandler() const;
 
-  const ModuleRegistry* GetModuleRegistry();
+  const ModuleRegistry* GetModuleRegistry() const;
 
   template <class T>
   T* GetDependency() const {