HSBC (HSBA.L) announced a $2.5 billion share buy-back and pared ambitions to grow dividend payouts and returns as it took pragmatic steps to soothe investors amid slowing growth in its home markets of Britain and Hong Kong. The lender’s London-listed shares were trading 3.6 percent higher at 0808 GMT (4:08 a.m. ET) after the buy-back took the sting out of …