Set mBrightness when needsComposite is zero

When needsComposite is zero in persistBrightness(), the mBrightness
needs to be updated to avoid unexpected skipping.

Bug: 244268674
Test: adb shell cmd device_state state 0 or 1 repeatly
Change-Id: Iccf925c1407e4be489da2dba521b93eee1b1c4b5
1 file changed