Settings: fix incorrect value in autobrightness adjustment

If the user drag the progress bar below the min value, the incorrect
setting will be saved since seekBar.setProgress code path does not
return to the "getItem(pos).backlight = ..." line.

Change-Id: I4796e22ba9c44315be92de4040f6cd8451bdf153
Merge branch 'jellybean' of https://github.com/XYAOSP/packages_apps_Settings into jellybean