binman: Correct init of entry in Entry class

This should not have an underscore. Drop it so that derived classes can
rely on it being set correctly.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/entry.py

@@ -95,7 +95,7 @@ class Entry(object):
         self.pad_after = 0
         self.offset_unset = False
         self.image_pos = None
-        self._expand_size = False
+        self.expand_size = False
         self.compress = 'none'
         self.missing = False
         self.external = False