How alcohol affects the male sperm is currently being studied. Whatever the effects are found to be, a father's drinking is not a fetal alcohol syndrome cause. Fetal alcohol syndrome and other fetal alcohol spectrum disorders are caused specifically by the mother's alcohol use during pregnancy.
However, the father's role is important. He can help the woman avoid drinking alcohol during pregnancy. He can encourage her abstinence from alcohol by avoiding social situations that involve drinking. He can also help her by avoiding alcohol himself.