wifi: rtw89: 8851b: configure to force 1 TX power value

RTL8851B is a chip with only single RF path, and it must use 1 TX power
value for transmission, so force 1 TX power value to prevent hardware
logic gets wrong TX power values randomly in certain samples.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230615130442.18116-6-pkshih@realtek.com