ath10k: allow empty ssid vdev config
It doesn't make much sense to reject a valid
firmware configuration combination.
Since SSID isn't known early on it might make
sense to allow driver to start vdev without SSID
and restart it later.
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>