This drupal.stackexchange post shows that a current patch that needs review and is slated for 1.0 release adds this functionality to Views:
View with entityreference: make exposed filter autocompleteView with entityreference: make exposed filter autocomplete
The related issue queue request is here:
https://drupal.org/node/1492260
The answer to your question is to apply the patch found in the issue queue. If you dont know how to do that -- now is a great time to learn something new about patch files, Linux, DrushMake or Git.