<?php

$query = db_select('field_config_instance', 'fci');
$query->join('field_config', 'fc', 'fci.field_name = fc.field_name');
$query
  ->fields('fci', array('entity_type', 'bundle', 'field_name'))
  ->condition('fc.type', array('taxonomy_term_reference'), 'IN')
  ->condition('fci.bundle', 'cv');
$result = $query->execute();

while ($r = $result->fetchObject()) {
  $instance = field_info_instance($r->entity_type, $r->field_name, $r->bundle);
  if ($instance['widget']['type'] != 'taxonomy_autocomplete') {
    $instance['widget']['type'] = 'taxonomy_autocomplete';
    field_update_instance($instance);
  }
}