Fix "Automatically sync app data" button state not changed

This issue is caused by mPreference is null.
(Not recovered when the fragment is recreated after configuration change.)

Mimic the PreferenceDialogFragmentCompat.getPreference() in AndroidX to
solve this issue.
https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:preference/preference/src/main/java/androidx/preference/PreferenceDialogFragmentCompat.java;l=176;drc=ca9feb3b73769089afbfd36b4d4a3d91239f9cd5

Ideally in the long term, we could use PreferenceDialogFragmentCompat
instead.

Fix: 218754949
Test: robotest & manual
Change-Id: I7fc8dd3b771aa45c91f915e25c8cc6c6afdd8d63