wifi: rtw89: coex: Correct A2DP exist variable source

When Wi-Fi enter and leave LPS, coexistence driver need to know
is there A2DP exist or not. And when Wi-Fi sleep in deep power save
state will not able to receive mailbox sent from Bluetooth. So update
the A2DP exist information from reading register.

Signed-off-by: Ching-Te Ku <ku920601@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/20230117114109.4298-7-pkshih@realtek.com