staging: wfx: simplify wfx_config()

Now that wfx_config() only handles IEEE80211_CONF_CHANGE_PS, it can be
simplified.
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-16-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/sta.c

@@ -1230,22 +1230,13 @@ int wfx_config(struct ieee80211_hw *hw, u32 changed)
 	struct wfx_dev *wdev = hw->priv;
 	struct wfx_vif *wvif;
 
-	// FIXME: Interface id should not been hardcoded
-	wvif = wdev_to_wvif(wdev, 0);
-	if (!wvif) {
-		WARN(1, "interface 0 does not exist anymore");
-		return 0;
-	}
-
-	mutex_lock(&wdev->conf_mutex);
 	if (changed & IEEE80211_CONF_CHANGE_PS) {
+		mutex_lock(&wdev->conf_mutex);
 		wvif = NULL;
 		while ((wvif = wvif_iterate(wdev, wvif)) != NULL)
 			ret = wfx_update_pm(wvif);
-		wvif = wdev_to_wvif(wdev, 0);
+		mutex_unlock(&wdev->conf_mutex);
 	}
-
-	mutex_unlock(&wdev->conf_mutex);
 	return ret;
 }