ath6kl: Normalize use of FW_DIR

kvalo: do the same changes for ar6004 hw1.2 as well

Cc: Kalle Valo <kvalo@qca.qualcomm.com>
Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>