Brightness mirror - fix multi-touch issue

The issue is that QSPanel get touch event while brightness mirros
is showing after density changes. This is because StatusBarWindowView
keeps the reference of detached brightness mirror view. We can refresh
it at onViewAdded function.

Test: manual(change device density > Check if can click QuickSettings
while dragging brightness slider.)

Change-Id: I646092abbc23b24bb91fc5c8525b12a143364b84