Doc: replace \o with \li

The \o QDoc command has been deprecated in QDoc for
Qt 5 and using it prints a QDoc warning.

Change-Id: Ibf0be59f3953bd731c2133cee3ec399e51df84a5
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>