Reset DWB color temperature when DWBC is disabled

Currently when DisplayWhiteBalanceController is disabled, it resets
internal states and disables related sensors. However, it does not
modify the display's color temperature. This results in the last color
temperature remaining in effect during Always on Display, even though
DWBC no longer controls it.

This change makes DWBC reset the display's color temperature to a
default value when it is disabled.

Bug 130262595
Test: manual

Change-Id: I066577d705cc9a518fe9196b0afd7374980816b3