ath9k: Check early for HW reset

chan_lock is not required for checking if
we are in the middle of a HW reset, so do it
early. This also removes the small window
where the lock is dropped and reacquired.

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