CRAS: alsa_io: return error if alsa asks for 0 frames.
CRAS: alsa_io: return error if alsa asks for 0 frames.

If snd_pcm_mmap_begin sets frames to 0 then return -EIO.  This can
happen if there is an error between the time get_avail_frames and
mmap_begin is called.

BUG=none
TEST=manual, play youtube while starting and stopping the WaveSynth
WebAudio demo in another window.  Previously this would cause
mmap_begin to set frames to 0

Change-Id: I95e2934d553e86e7c1eb323f56dbb3948e776350
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd