Make Reference::get follow const rules

Instead of having T* Reference::get() const, this change brings
const T* Reference::get() const and
      T* Reference::get()

Test: mma
Change-Id: I1c8834467acffd426c25aa9c0661c290a05d7a52
diff --git a/TypeDef.h b/TypeDef.h
index e6af502..cb11997 100644
--- a/TypeDef.h
+++ b/TypeDef.h
@@ -30,7 +30,8 @@
 
     std::string typeName() const override;
 
-    Type* referencedType() const;
+    Type* referencedType();
+    const Type* referencedType() const;
 
     bool isInterface() const override;
     bool isEnum() const override;