binman: Fix up ProcessUpdateContents error and comments

This function raises an exception with its arguments around the wrong way
so the message is incorrect. Fix this as well as a few minor comment
problems.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index c675299..1c91734 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -1223,7 +1223,7 @@
         with self.assertRaises(ValueError) as e:
             self._DoReadFile('059_change_size.dts', True)
         self.assertIn("Node '/binman/_testing': Cannot update entry size from "
-                      '2 to 1', str(e.exception))
+                      '1 to 2', str(e.exception))
 
     def testUpdateFdt(self):
         """Test that we can update the device tree with offset/size info"""