It is a dream come true for a first-time novelist: a call from Oprah Winfrey with the news that your novel has been chosen for her book club. That dream recently came true for Ayana Mathis, the author of “The Twelve Tribes of Hattie” (Alfred A. Knopf). Ms. Winfrey announced Wednesday that she has chosen the novel for the book club famously associated with her former TV talk show. In response to the endorsement, the publishers increased the book’s first printing to 125,000 copies.