[ALSA] Fix PCM write blocking

The snd_pcm_lib_write1() may block in some weird condition:
  - the stream isn't started
  - avail_min is big (e.g. period size)
  - partial write up to buffer_size - avail_min
The patch fixes this invalid blocking problem.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>