Maybe you need to install the appropriate “external” package wifi-qcom-ac wireless package.
Starting from 7.13.x it is a separate package:
http://forum.mikrotik.com/t/7-13-wireless-package-split-question/172049/1
http://forum.mikrotik.com/t/v7-13-5-stable-is-released/171923/1
EDIT: post corrected.