Make doze vars volatile to be thread safe

Brightness changes may be requested on the background thread
around the same time as a screen state change. Make these
doze variables volatile so that when doze is updated,
the correct screen state and brightness values are used.

Bug: 342529814
Flag: EXEMPT bugfix
Test: screen off with UDFPS enrolled; trigger quick
pickup gesture. wait for screen to time out back to screen
off in 6s. Repeat 20 times. Observe screen always
turns back off.

Change-Id: Ie66014ee100a17b88c451e667feda58df9fc5942