wifi: rtw88: Fix rtw_desc_to_mcsrate() to handle MCS16-31

This function translates the rate number reported by the hardware into
something mac80211 can understand. It was ignoring the 3SS and 4SS HT
rates. Translate them too.

Also set *nss to 0 for the HT rates, just to make sure it's
initialised.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/d0a5a86b-4869-47f6-a5a7-01c0f987cc7f@gmail.com