ath9k: Check early for multi-vif/STA conditions

If multiple interfaces are active or there is no
associated station interface, bail out early and
return 1 so that mac80211 can proceed with the normal
suspend routine.

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