[audio] Add wtf if audioserver not up on start

If audioserver isn't available during the initial boot of AudioService,
the system is likely to hit unpredictable issues. Add a wtf to
improve visibility of those cases.

Test: boot
Bug: 357468728
Flag: EXEMPT bugfix
Change-Id: I8e55ddacf85f0380ed662a1cc309d871a5431303