Settings: fix blacklist settings crash

On a device rotate, the MultiSelectListPreference would try and restore
its state since the preferences aren't persisted. Clear the persisted
flag so the MultiSelectPreference doesn't try and restore the states, as
they get populated in onResume().

Change-Id: I0d0304e2367ade66e35ae7df432575d13ed0993e
Signed-off-by: Roman Birg <roman@cyngn.com>