Do not deactivate the proximity sensor until after the sensor returns negative.

This ensures that we do not get cheek presses immediately after a call is ended.
Fixes bug b/2246824 (prox sensor subtleties when call ends)

Change-Id: I97d39b7689d9ea2e94ea9aceeb93bf15228ec095
Signed-off-by: Mike Lockwood <lockwood@android.com>