ath10k: fix offchannel cancel failures

When mac80211 requests driver to cancel a hw roc
the driver must not call the expired() callback or
else roc will fail in some cases depending on how
things get scheduled.

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