net: ethernet: ti: am65-cpsw: fix CONFIG_PM #ifdef

The #ifdef check is incorrect and leads to a warning:

drivers/net/ethernet/ti/am65-cpsw-nuss.c:1679:13: error: 'am65_cpsw_nuss_remove_rx_chns' defined but not used [-Werror=unused-function]
 1679 | static void am65_cpsw_nuss_remove_rx_chns(void *data)

It's better to remove the #ifdef here and use the modern
SYSTEM_SLEEP_PM_OPS() macro instead.

Fixes: 24bc19b ("net: ethernet: ti: am65-cpsw: Add suspend/resume support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Link: https://lore.kernel.org/r/20221215163918.611609-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/ti/am65-cpsw-nuss.c

@@ -2878,7 +2878,6 @@ static int am65_cpsw_nuss_remove(struct platform_device *pdev)
 	return 0;
 }
 
-#ifdef CONFIG_PM_SLEEP
 static int am65_cpsw_nuss_suspend(struct device *dev)
 {
 	struct am65_cpsw_common *common = dev_get_drvdata(dev);
@@ -2964,10 +2963,9 @@ static int am65_cpsw_nuss_resume(struct device *dev)
 
 	return 0;
 }
-#endif /* CONFIG_PM_SLEEP */
 
 static const struct dev_pm_ops am65_cpsw_nuss_dev_pm_ops = {
-	SET_SYSTEM_SLEEP_PM_OPS(am65_cpsw_nuss_suspend, am65_cpsw_nuss_resume)
+	SYSTEM_SLEEP_PM_OPS(am65_cpsw_nuss_suspend, am65_cpsw_nuss_resume)
 };
 
 static struct platform_driver am65_cpsw_nuss_driver = {