CEE MARKETS-Stocks rebound, shrug off Polish PM's warning to EU

* Regional stocks dip initially on news about PZU, OTP Bank * PZU fires CEO, Groupama places OTP shares at low price * Polish PM says may block the EU's Rome declaration * Polish bonds firm slightly ahead of auction By Sandor Peto BUDAPEST, March 23 (Reuters) - Central European stocks rebounded on Thursday, tracking Western European peers and shrugging off a warning from Polish Prime Minister Beata Szydlo that her country may block a political roadmap for the European Un