Add lost prefController to WifiTetherSettings

One controller is lost during a refactor(ag/4774003), this CL adds
it back.

Change-Id: Ie50a3ac009f302d4fd7a179117fe026031cc1ae8
Fixes: 122235175
Test: RunSettingsRoboTests

src/com/android/settings/wifi/tether/WifiTetherSettings.java

@@ -178,6 +178,8 @@ public class WifiTetherSettings extends RestrictedDashboardFragment
         controllers.add(new WifiTetherSecurityPreferenceController(context, listener));
         controllers.add(new WifiTetherPasswordPreferenceController(context, listener));
         controllers.add(new WifiTetherApBandPreferenceController(context, listener));
+        controllers.add(
+                new WifiTetherAutoOffPreferenceController(context, KEY_WIFI_TETHER_AUTO_OFF));
 
         return controllers;
     }