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/control.py b/tools/binman/control.py
index 8f7f906..ce25eb5 100644
--- a/tools/binman/control.py
+++ b/tools/binman/control.py
@@ -131,7 +131,7 @@
 
             if options.image:
                 skip = []
-                for name, image in images.iteritems():
+                for name, image in images.items():
                     if name not in options.image:
                         del images[name]
                         skip.append(name)