patman: Use items() instead of iteritems()

Python 3 requires this, and Python 2 allows it. Convert the code over to
ensure compatibility with Python 3.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/settings.py b/tools/patman/settings.py
index ea2bc74..07bf6a6 100644
--- a/tools/patman/settings.py
+++ b/tools/patman/settings.py
@@ -163,7 +163,7 @@
         item_dict = dict(top_items)
         item_dict.update(project_items)
         return {(self._to_unicode(item), self._to_unicode(val))
-                for item, val in item_dict.iteritems()}
+                for item, val in item_dict.items()}
 
 def ReadGitAliases(fname):
     """Read a git alias file. This is in the form used by git: