ath10k: fix multi BSSID with WPA on FW 10.1

FW 10.1 seems to require the default key index to
be updated to point to group key after it is
installed. Otherwise Txed frames are corrupted.

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