Fix screen-on speed during phone call

RampAnimator was being passed -1.0f (PowerManager.BRIGHTNESS_OFF) and animating from that. This change ensures only valid brightness values are passed to it. brightnessState includes values such as off and invalid, which shouldn't be animated to. brightnessValues represent a value from PowerManager.BRIGHTNESS_MIN to PowerManager.BRIGHTNESS_MAX (0.0f - 1.0f).

Bug: 152171816

Test: manual
Change-Id: I2e7a80d50e4b52817959c120e6ee96a4186c2f8b