wifi: rtw89: 8851b: fix TX path to path A for one RF path chip

For two RF paths chips, we normally set path B as main path by default.
8851B has single one RF path, so set TX path to A and set mapping of
path B to 0.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230330133324.19538-3-pkshih@realtek.com