ucm: initialize mgr->once_list
ucm: initialize mgr->once_list

BugLink: https://github.com/alsa-project/alsa-lib/pull/50

Signed-off-by: Jaroslav Kysela <72edd5e1a572f82f059ccbb83c92b74d6cb051ff@perex.cz>

tiwai/alsa-lib,alsa-project/alsa-lib,alsa-project/alsa-lib,alsa-project/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib,takaswie/alsa-lib,alsa-project/alsa-lib