python3: iteritems does not exist

Change iteritems to items, which is slightly slower
on python2 but exists in both.  None of the maps manipulated
by this program are large enough for the items vs iteritems
to be a concern.

Change-Id: I63032ddde53a116431cc2cbe01828448a4d4f328
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/callouts/callouts-gen.mako.hpp b/callouts/callouts-gen.mako.hpp
index 7d28a3a..285092e 100644
--- a/callouts/callouts-gen.mako.hpp
+++ b/callouts/callouts-gen.mako.hpp
@@ -14,7 +14,7 @@
 
 constexpr auto callouts =
 {
-% for key, value in sorted(calloutsMap.iteritems()):
+% for key, value in sorted(calloutsMap.items()):
     std::make_tuple("${key}", "${value}"),
 % endfor
 };