The PCM xrun injection triggers directly snd_pcm_stop() without the
standard xrun handler, hence it's not recorded on the event buffer.
Ditto for snd_pcm_stop_xrun() call and SNDRV_PCM_IOCTL_XRUN ioctl.
They are inconvenient from the debugging POV.

Let's make them to trigger XRUN via the standard helper more
consistently.
Signed-off-by: Takashi Iwai <tiwai@suse.de>