Make terminate_voice() actually do at all what it's supposed to do:
instantly and completely shut down the note.

The bogus behavior was mostly harmless, as usually the voice is freed
right afterwards, which implicitly terminates it anyway.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230518140339.3722308-2-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>