ath10k: fix firmware recovery with ap interface

Beacon data wasn't properly cleared during early
phase of recovery. This in turn caused firmware to
crash because the beacon data was submitted before
vdevs were fully re-configured. Ultimately the
device was considered wedged and nothing worked
until driver was reloaded.

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