drivers: wifi: siwx91x: Handle error case in power save mode

Power save is not supported in AP mode. This commit ensures that
`-EINVAL` is returned instead of success, preventing incorrect behavior.

(cherry picked from commit de6395d)

Original-Signed-off-by: Arunmani Alagarsamy <[email protected]>
GitOrigin-RevId: de6395d
Cr-Build-Id: 8712973260362085153
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8712973260362085153
Copybot-Job-Name: zephyr-main-copybot-downstream
Change-Id: I83507875464e9490e24aca56b7b641f64d1bc6e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/6621872
Tested-by: ChromeOS Copybot <[email protected]>
Tested-by: Dawid Niedźwiecki <[email protected]>
Reviewed-by: Dawid Niedźwiecki <[email protected]>
Commit-Queue: Dawid Niedźwiecki <[email protected]>

Author: Arunmani Alagarsamy

drivers/wifi/siwx91x/siwx91x_wifi.c

@@ -282,11 +282,13 @@ static int siwx91x_apply_power_save(struct siwx91x_dev *sidev)
 
 	interface = sl_wifi_get_default_interface();
 	if (FIELD_GET(SIWX91X_INTERFACE_MASK, interface) != SL_WIFI_CLIENT_INTERFACE) {
-		return 0;
+		LOG_ERR("Wi-Fi not in station mode");
+		return -EINVAL;
 	}
 
 	if (sidev->state == WIFI_STATE_INTERFACE_DISABLED) {
-		return 0;
+		LOG_ERR("Command given in invalid state");
+		return -EINVAL;
 	}
 
 	sl_wifi_get_performance_profile(&sl_ps_profile);