wifi: rtw89: correct 5 MHz mask setting

Use primary channel index to determine which 5 MHz mask should be enable.
This mask is used to prevent noise from channel edge to effect CCA
threshold in wide bandwidth (>= 40 MHZ).

Fixes: 1b00e923 ("rtw89: 8852c: add set channel of BB part")
Fixes: 6b069898 ("wifi: rtw89: 8852b: add chip_ops::set_channel")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Huang <echuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230406072841.8308-1-pkshih@realtek.com