Minor kotlin cleanup

Use regular function instead of expression functions for Unit return
types.
go/kotlin/practices/expression-functions#unit-functions

Flag: com.android.wm.shell.enable_bubble_bar
Bug: 281083629
Test: no-op change. just verify this builds
Change-Id: Ie13fdad5f33bb4cda9e5e85e2fb4394131d3c63f