The async callback mechanism in ALSA is prone to deadlock.
There was already a timer fallback mechanism that appears to be
sufficient.
Task-number: QTBUG-39677
Change-Id: I44b59e6b16eea1c9c4eeb6967335ce4f468cf3c4
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>