wifi: rtw89: add RSSI statistics for the case of antenna diversity to debugfs

RSSI strength is only from PHY path A, but there are two antenna for the
module which supports antenna diversity. So, set RSSI value to index 1 of
RSSI array if current antenna is on antenna B. Then, debugfs can show
two RSSI values with a asterisk mark on selected antenna.

  RSSI: -23 dBm (raw=174, prev=173) [-26, -23*]

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230418012820.5139-4-pkshih@realtek.com