usb: renesas_usbhs: mark PM functions as __maybe_unused

Without CONFIG_PM, we get a new build warning here:

drivers/usb/renesas_usbhs/common.c:860:12: error: 'usbhsc_resume' defined but not used [-Werror=unused-function]
 static int usbhsc_resume(struct device *dev)
            ^~~~~~~~~~~~~
drivers/usb/renesas_usbhs/common.c:844:12: error: 'usbhsc_suspend' defined but not used [-Werror=unused-function]
 static int usbhsc_suspend(struct device *dev)
            ^~~~~~~~~~~~~~

Fixes: d54d334e ("usb: renesas_usbhs: Use SIMPLE_DEV_PM_OPS macro")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/renesas_usbhs/common.c

@@ -841,7 +841,7 @@ static int usbhs_remove(struct platform_device *pdev)
 	return 0;
 }
 
-static int usbhsc_suspend(struct device *dev)
+static __maybe_unused int usbhsc_suspend(struct device *dev)
 {
 	struct usbhs_priv *priv = dev_get_drvdata(dev);
 	struct usbhs_mod *mod = usbhs_mod_get_current(priv);
@@ -857,7 +857,7 @@ static int usbhsc_suspend(struct device *dev)
 	return 0;
 }
 
-static int usbhsc_resume(struct device *dev)
+static __maybe_unused int usbhsc_resume(struct device *dev)
 {
 	struct usbhs_priv *priv = dev_get_drvdata(dev);
 	struct platform_device *pdev = usbhs_priv_to_pdev(priv);