lineage-iosched: restorecon scheduler tuneables before touching them

* LineageOS/android_system_sepolicy@0e3235f45d removed open, read,
  and write for init to general sysfs types. As schedulers are
  changed, the related directories gets dynamically torn-down and
  rebuilt, but they lacks proper contexts. We need to make sure the
  context is correct before init can write to these nodes.

Change-Id: Ic6f4567c173799bc56ecccc217040392f73aeaba