Fill in a stub parameter to startKeyguardExit

startKeyguardExitAnimation doesn't use this any more on aosp but it's
cleaner to fill it in with a correct value anyway in case it is used
in the future or downstream

Change-Id: Ic23fff0f14b9278be2362cfb1da307821ae3851e
Test: N/A
Bug: 343598832
Flag: com.android.window.flags.keyguard_going_away_timeout