wcn36xx: Cache nv to avoid request_firmware on resume path

If wowlan if off mac80211 will stop / start the driver on suspend /
resume. This causes problems on resume since request_firmware is called
from start. Fix this by caching the nv.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>