wcn36xx: Use consistent name for private vif

Some code used priv_vif and some used vif_priv. Convert all to vif_priv
for consistency.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>