avoid shadowing in salt.utils.xdg_config_dir()

************* Module salt.utils.xdg
salt/utils/xdg.py:13: [W0621(redefined-outer-name), xdg_config_dir] Redefining name 'xdg_config_dir' from outer scope (line 8)
Merge pull request #12717 from hulu/xdg-shadowing

avoid shadowing in salt.utils.xdg_config_dir()