Synchronize VibrationService

There was a race around the mCurrentVibration field.
Now all access to this field is protected with synchronized() blocks

Bug: 72685111
Test: RUN_ERROR_PRONE shows no GuardedBy errors in VibrationService
Change-Id: I303c30763b4dea7a82e2ec2a27f978c4b1d413ea
1 file changed