Thanks for your answers guys !
By the company said : if there is two information in the Atis; ALWAYS take the most restrictive (= more safety). So, when it's DRY and there is a braking action mentionned, we have to take the braking action into consideration.
Reason is that we, as stupid pilots, are not able to determine if a dry runway has a perfect , good, medium or poor braking action, so we have to rely on the professionnal people who mesure the BA.
That's a bit strange, but who can complain that our company decide to go on the safe side ?