Feb 17 (Reuters) - Citigroup Inc cut Chief Executive Michael Corbat's compensation by 6 percent to $15.5 million in 2016, a year in which the bank fell short of profitability and efficiency goals and saw one-third of voting shareholders disapprove of the company's prior executive compensation. Corbat got a base salary of $1.5 million, a $4.2 million cash incentive and $9.8 million of deferred stock and instruments tied to stock prices, according to a filing by the company on Friday. (Repo