QtIFW

Doc: add \value commands to generate docs properly

for UpdateOperation::Error enum

Change-Id: Ib8b019bfe4aa8ab541dd37e8d96e06eb98d3e23b
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>