ath10k: fix hw roc expiration

It is not guaranteed firmware will switch to
foreign channel immediately after starting scan
sequence. To account for that don't use duration
parameter for scan time. Instead request insanely
long scan and use timeout worker to cancel it from
driver.

This should improve P2P reliability a bit.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>