wlcore: allow elp during wowlan suspend

when enabling wowlan and entering suspend the last write to the firmware
allowing it to go into elp mode was not completing before suspend, leaving
the firmware running in full active mode consuming high power.
Use an immediate call instead of a work queue for this last access
allowing the firmware to go into power save during wowlan uspend.

Signed-off-by: Eyal Reizer <eyalr@ti.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>