SystemUI: status bar brightness: store value as int

Non-automatic brightness value is stored as int, not float.

Symptom: adjust the brightness in the status bar, the brightness
         slider in the notification bar will always be set to full

Change-Id: I5f9a6e97bae2c44c3aff7c9222186a6dbda5d902
Signed-off-by: Chet Kener <Cl3Kener@gmail.com>