Fixing notifications background in split shade mode

Notification background was not showing up when going from lockscreen to
shade directly with swipe down. ScrimState is changed then and only in
SHADE_LOCKED notification scrim alpha should depend on interpolated
fraction

Fixes: 186864180
Test: manual
Change-Id: I75468a92a6d0dd27c32b2eb5c5b0f90e48a4ff67