Use pref's layoutRes to bindViewHolder in tests

If the ViewHolder isn't created with the expected layout resource that
matches the Preference's layout resource, it would cause NPE when trying
to use the view.

Fix: 370776669
Test: atest SelectorWithWidgetPreferenceTest
Flag: EXEMPT test only

Change-Id: I757d2e17fb389a02189d950e058ab2d392d80fe0