Make DatastoreAccess::getItems const

I want to use this method in other const methods.

Change-Id: I32ff3fd8f0e77dbcea9b83b8ab8da99c1aa41f17
diff --git a/tests/datastoreaccess_mock.hpp b/tests/datastoreaccess_mock.hpp
index 8252d04..a495b99 100644
--- a/tests/datastoreaccess_mock.hpp
+++ b/tests/datastoreaccess_mock.hpp
@@ -19,7 +19,7 @@
 }
 
 class MockDatastoreAccess : public trompeloeil::mock_interface<DatastoreAccess> {
-    IMPLEMENT_MOCK1(getItems);
+    IMPLEMENT_CONST_MOCK1(getItems);
     IMPLEMENT_MOCK2(setLeaf);
     IMPLEMENT_MOCK1(createItem);
     IMPLEMENT_MOCK1(deleteItem);