binman: 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/binman/ftest.py b/tools/binman/ftest.py
index daea1ea..7cf1752 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -214,7 +214,7 @@
         if verbosity is not None:
             args.append('-v%d' % verbosity)
         if entry_args:
-            for arg, value in entry_args.iteritems():
+            for arg, value in entry_args.items():
                 args.append('-a%s=%s' % (arg, value))
         if images:
             for image in images: