ath9k: fix the assignment of hw queues for mesh interface

We need to assign the hw queues for mesh interface. Otherwise,
we are not able to bring up the mesh interface due to the
IEEE80211_INVAL_HW_QUEUE error.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>