MADRID (Reuters) – Spain’s BBVA said on Thursday it had secured the regulatory approval needed to launch a voluntary takeover bid for the 50.15% stake it does not already own in its Turkish unit Garanti. On Nov. 15, BBVA offered to buy the remaining stake in Garanti and established a maximum price of 25.697 billion Turkish lira ($2.03 billion), or 12.20 lira per share, should all Garanti shareholders sell their shares. The deal then represented a premium of 15%, but since then, a weaker Turkish lira has reduced the price of its deal in euros. The offer would now be worth 1.6 billion euros, dow…