Bug 1464003 - Refresh sync preference after rebuilding the list. r=Grisha

Differential Revision: https://phabricator.services.mozilla.com/D15209

--HG--
extra : moz-landing-system : lando

mobile/android/base/java/org/mozilla/gecko/preferences/GeckoPreferenceFragment.java

@@ -201,6 +201,7 @@ public class GeckoPreferenceFragment extends PreferenceFragment {
             // Rebuild the list to reflect the current locale.
             getPreferenceScreen().removeAll();
             addPreferencesFromResource(getResource());
+            syncPreference = (SyncPreference) findPreference(GeckoPreferences.PREFS_SYNC);
         }
 
         // Fix the parent title regardless.