aston villa face liverpool at wembley in the fa cup semi-final on sunday .
liverpool will have to keep villa 's in-form christian benteke quiet .
the belgium international has scored eight goals in six games for villa .
striker says that new manager tim sherwood has given him freedom .
benteke struggled for form earlier this season after recovering from injury .
a year ago he ruptured his achilles and missed the world cup .
benteke returned in october but did not hit top gear straight away .