ALSA: timer: Fix double unlink of active_list

ALSA: timer: Fix double unlink of active_list

ALSA timer instance object has a couple of linked lists and they are
unlinked unconditionally at snd_timer_stop().  Meanwhile
snd_timer_interrupt() unlinks it, but it calls list_del() which leaves
the element list itself unchanged.  This ends up with unlinking twice,
and it was caught by syzkaller fuzzer.

The fix is to use list_del_init() variant properly there, too.

Reported-by: Dmitry Vyukov <[email protected]>
Tested-by: Dmitry Vyukov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>