qapi/introspect.py: Unify return type of _make_tree()

Returning two different types conditionally can be complicated to
type. Return one type for consistency.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210216021809.134886-7-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/introspect.py

@@ -29,9 +29,7 @@ def _make_tree(obj, ifcond, extra=None):
         extra = {}
     if ifcond:
         extra['if'] = ifcond
-    if extra:
-        return (obj, extra)
-    return obj
+    return (obj, extra)
 
 
 def _tree_to_qlit(obj, level=0, dict_value=False):