ath10k: move free_vdev_map initialization

This is necessary for hw reconfiguration to work.
Since mac80211 is not calling remove_interface()
is such case we must reset free_vdev_map.

Also use a define instead of a hardcoded value for
vdev map initialization.

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