wifi: rtw88: Fix rtw_init_ht_cap() for RTL8814AU

Set the RX mask and the highest RX rate according to the number of
spatial streams the chip can receive. For RTL8814AU that is 3.

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/4e786f50-ed1c-4387-8b28-e6ff00e35e81@gmail.com