issue snd_pcm_start() when capturing audio

snd_pcm_start() starts the capture process and ensures that the events
are delivered to the poll handler. Without the call, capture can be started
only when there is simultaneous playback running.

Signed-off-by: Jindrich Makovicka <makovick@gmail.com>
Signed-off-by: malc <av1474@comtv.ru>