Use correct brightness when manual brightness is enabled.

We want to use whatever the current brightness setting value is, not
whatever the user set last. This means that we'll have a reasonable
value at first boot and we won't get weird brightness jumps when users
disable autobrightness.

Fixes: 72508527
Test: Manual

Change-Id: I4178593f91b231ebcffb6e2104c515e557d975fc