wcn36xx: Fix HT40 capability for 2Ghz band

All wcn36xx controllers are supposed to support HT40 (and SGI40),
This doubles the maximum bitrate/throughput with compatible APs.

Tested with wcn3620 & wcn3680B.

Cc: stable@vger.kernel.org
Fixes: 8e84c258

 ("wcn36xx: mac80211 driver for Qualcomm WCN3660/WCN3680 hardware")
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1634737133-22336-1-git-send-email-loic.poulain@linaro.org