wcn36xx: Specify ieee80211_rx_status.nss

Specify the number of spatial streams in ieee80211_rx_status. For non VHT
data-rates the wireless core doesn't care about this field, however for VHT
data-rates it does.

Every version of wcn36xx has one spatial stream, so specify nss for
wcn3620, wcn3660 and wcn3680 now.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200829033846.2167619-7-bryan.odonoghue@linaro.org