Clamp display brightness in AOD

AOD display brightness should respect user settings, otherwise screen can
get brighter after pressing the power button.

Test: manual
Test: runstest -x packages/SystemUI/tests/src/com/android/systemui/doze/DozeScreenBrightnessTest.java
Change-Id: I4f43202fe5c8e844655ec533d46d2d472502a33e
Fixes: 111080388