wcn36xx: Add VHT rates to wcn36xx_update_allowed_rates()

This commit adds VHT rates to the wcn36xx_update_allowed_rates() routine.
Thus allowing the driver to latch the declared rates and transmit them to
the firmware in the same way as other 80211.n rates are.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200910150822.2179261-4-bryan.odonoghue@linaro.org