ath9k: fix beacon descriptor

The tx interrupt for beacon queue is configured only for edma chips.
As the edma chip does not support per descriptor interrupt, no need to
set INTREQ for every beacon descriptor. And also clear ps filter for
beacon frame.

Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>