wifi: rtw89: mac: refine SER setting during WiFi CPU power on

Don't enable firmware debug mode to prevent SER flow stuck due to fail
to reset payload buffer, and clear HALT_C2H_INT to avoid handling
unexpected interrupt at beginning.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231204080751.15354-6-pkshih@realtek.com