migration: process_incoming_migration_co(): rework error reporting Unify error reporting in the function. This simplifies the following commit, which will not-exit-on-error behavior variant to the function. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Fabiano Rosas <farosas@suse.de>