wifi: wfx: fix power_save setting when AP is stopped

The WF200 allow to start two network interfaces (one AP, one station) on
two different channels. Since magic does not exist, it only works if the
station interface enables power save.

Thus, the driver detects this case and enforce power save as necessary.

This patch fixes the case where the AP interface is stopped and it is no
more necessary to enforce power saving on the station interface.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231004172843.195332-2-jerome.pouiller@silabs.com