The PCM core should perform the sync for the pending stop operations
at disconnection.  Otherwise it may lead to unexpected access.

Currently the old user of sync_stop, USB-audio driver, has its own
sync, so this isn't needed, but it's better to guarantee the sync in
the PCM core level.

This patch adds the missing sync_stop call at PCM disconnection
callback.  It also assures the IRQ sync if it's specified in the
card.  snd_pcm_sync_stop() is slightly modified to be called also for
any PCM substream object now.

Fixes: 1e850bee ("ALSA: pcm: Add the support for sync-stop operation")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210206203656.15959-2-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>