Keep DOZE_INITIAL brightness in setting

We don't want to fall back to the last interactive brightness when the screen turns on because it might be brighter than the brightness applied shortly after, when a lux sample is available.

Bug: 336000148
Test: See that there's no bright flash when going from AOD to ON
Test: atest DisplayPowerControllerTest
Change-Id: I5fed20f6b4d2de3821f52ac06dc21c0dbe287aac