wifi: rtw88: add flag check before enter or leave IPS

Enter or leave IPS controlled by mac80211 before driver support HW
scan. After support HW scan, driver need to control IPS before start
HW scan and scan complete, but mac80211 also ask driver enter or leave
IPS. Therefore, we add flag check in IPS to prevent entering or
leaving IPS twice.

Signed-off-by: Chih-Kang Chang <gary.chang@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/20220809084107.38137-7-pkshih@realtek.com