ath9k_htc: Avoid setting QoS control for non-QoS frames

Setting tid information in the TX header is required only for QoS
frames. Not handling this case causes severe data loss with some APs.

Cc: stable@kernel.org
Signed-off-by: Rajkumar Manoharan <rmanoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>