Only clamp off brightness from DOZE_INITIALIZED

When the display times out, the power manager
briefly decreases the brightness of the display
before transitioning to AOD, so we don't want
to immediately increase the brightness to the AOD
brightness. However, for all other state changes
we don't need to take into account the screen
off brightness clamping.

Test: atest DozeScreenBrightnessTest
Fixes: 219675877
Change-Id: I8d25096f45cdb18717cc3d110bf5949f202c3982