security: code cleanup and doxygen improvements in tpm::BackEndOsx

Change-Id: I6d6d77ab315a10c280e7643d4cec5269ed10fe5e
diff --git a/src/security/tpm/key-handle-osx.hpp b/src/security/tpm/key-handle-osx.hpp
index a6e1484..8b0e308 100644
--- a/src/security/tpm/key-handle-osx.hpp
+++ b/src/security/tpm/key-handle-osx.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2017 Regents of the University of California.
+ * Copyright (c) 2013-2018 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -23,12 +23,13 @@
 #define NDN_SECURITY_TPM_KEY_HANDLE_OSX_HPP
 
 #include "key-handle.hpp"
-#include "key-ref-osx.hpp"
 
 #ifndef NDN_CXX_HAVE_OSX_FRAMEWORKS
 #error "This file should not be compiled ..."
 #endif
 
+#include "key-ref-osx.hpp"
+
 namespace ndn {
 namespace security {
 namespace tpm {