By Diadie Ba and NDIAGA THIAM DAKAR, May 4 (Reuters) – Senegalese President Bassirou Diomaye Faye said the ruling party is on a path that could lead to its downfall but that the party’s leader, Prime Minister Ousmane Sonko, will remain in his post if he keeps “doing his job properly”.Faye’s comments, aired on state television late Saturday, come amid persistent speculation that the two men’s political alliance is on the rocks and as the West African country faces growing economic challenges...