ath9k: Set keep awake timer

When MCI is enabled and WoW sleep is enabled,
make sure that the RTC keep awake timer is set
with the required value. This is also required
when the AR_WA is programmed.

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