wifi: rtw89: coex: Get Bluetooth desired version by WiFi firmware version

Because when Wi-Fi/Bluetooth want to communicate with each other, their
contact window are their firmware. So the desired version code is more
reasonable to change with firmware version.

Signed-off-by: Ching-Te Ku <ku920601@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250616090252.51098-6-pkshih@realtek.com