SystemUI: fix status bar brightness slider eating events

In some cases it would eat the event and not lose focus to the rest of
the system.

Change-Id: I94d532d09ea762edf7ac037043ed023caf42c401
Signed-off-by: Roman Birg <roman@cyngn.com>
Signed-off-by: Chet Kener <Cl3Kener@gmail.com>