ath9k: Remove unnecessary AMPDU check at tx status

Fill the ampdu_[ack]_len for both aggregation and normal frames.
So that we could avoid unnecesary conditional at tx status.

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