ALSA: timer: Unconditionally unlink slave instances, too

Like the previous fix (commit c0317c0e "ALSA: timer: Fix
use-after-free problem"), we have to unlink slave timer instances
immediately at snd_timer_stop(), too.  Otherwise it may leave a stale
entry in the list if the slave instance is freed before actually
running.

Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20211105091517.21733-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>