ath6kl: Configure 0 as rsn cap when it is not there in rsn ie

Currently rsn capability is not set when it is not available in
rsn IE. Set it to 0 in firmware when it is not there in the ie to
make sure host and target are consistent.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>