Fixed a bug where notifications could be dimmable

Because of a delayed call, notifications could become
dimmed again after the unlock.

Test: runtest -x packages/SystemUI/tests/src/com/android/systemui/statusbar/stack/NotificationStackScrollLayoutTest.java
Change-Id: I76e847cf6d3c8a34ca4b6dd16b1c8e13ddfe4993
Fixes: 64868746