ath10k: make hw roc more reliable

With P2P concurrency requested hw roc duration
time can be very small. Some firmware revisions
refuse scan requests with too small channel dwell
time.

This prevents messages like, e.g. with connected
STA vif and performing P2P Find:

 ath10k_pci 0000:00:05.0: failed to switch to channel for roc scan
 ieee80211 phy3: failed to start next HW ROC (-110)

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