SystemUI: Update resources on theme change in shade header

So, it will update color after updating text appearance
as like onDensityOrFontScaleChanged().

Fixes QS carrier text color on theme changes after QPR3.

Change-Id: I6e0c2b6094d74b12d029a3a4dce05e8e27d654ea

onThemeChanged() will be called after onUiModeChanged()
on device light/dark mode changes.
So don't do twice as it produce race condition
that shows wrong color for carrier text again.

Change-Id: Ie74b67483cad8164478cc5fe36fa07abe2a3b3bf