The V4L2 async wasn't part of the documentation build. Fix this.
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: NNiklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Acked-by: NHans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>