Not only clean up enabled voices but any registered one. Backends like
pulsaudio rely on unconditional fini handler invocations.

This fixes "Memory pool destroyed but not all memory blocks freed!"
warnings on VM shutdowns when pa is used and lockups of QEMU on shutdown
as it got stuck on some pa-internal synchronization point.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: malc <av1474@comtv.ru>