rtw88: fix NSS of hw_cap

8822C is a 2x2 11ac chip, and then NSS must be less or equal to 2. However,
current nss of hw cap is 3, likes
	hw cap: hci=0x0f, bw=0x07, ptcl=0x03, ant_num=7, nss=3

This commit adds constraint to make sure NSS <= rf_path_num, and result
looks like
	hw cap: hci=0x0f, bw=0x07, ptcl=0x03, ant_num=7, nss=2

Fixes: e3037485

 ("rtw88: new Realtek 802.11ac driver")
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>