ALSA: pcm: Use deferred fasync helper

For avoiding the potential deadlock via kill_fasync() call, use the
new fasync helpers to defer the invocation from timer API.  Note that
it's merely a workaround.

Reported-by:  <syzbot+8285e973a41b5aa68902@syzkaller.appspotmail.com>
Reported-by:  <syzbot+669c9abf11a6a011dd09@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/r/20220728125945.29533-4-tiwai@suse.de


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