ath9k: Return early for error conditions

Do not try to cancel work instances and ANI when
the device is not present or WOW triggers are
not configured. Bail out early and use ath_err()
for such error conditions.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>