Fix a bug in command line option parsing (#2941)

option should not be overridden by subsequent options of the same module.

ppdet/utils/cli.py

@@ -68,6 +68,7 @@ class ArgsParser(ArgumentParser):
                 config[k] = yaml.load(v, Loader=yaml.Loader)
             else:
                 keys = k.split('.')
+                if keys[0] not in config:
                     config[keys[0]] = {}
                 cur = config[keys[0]]
                 for idx, key in enumerate(keys[1:]):