BrightnessMirror: When reinflating, notify QSPanel

Fixes an issue where after reinflating the brightness mirror,
the QSPanel was not notified.

Change-Id: I3974f31c2d3c67b5a283b10690cb103ca13fff6a
Fixes: 64460731
Test: Change to white / black wallpaper (opposite of current); verify brightness slider works.