SystemUI: Fix QS header clock color

Now that we're flipping QS colors by theme (dark/light), we can no longer
rely on wallpaper colors for QS clock. Instead, we now can rely on clock color
being updated correctly on QS re-inflation (via
QuickStatusBarHeader.updateResources).

Change-Id: Icdf2484793cb63b7c0ab6ab87e94185e6bdc9ca4