usb: xhci: avoid warning for !PM_SLEEP

If we build a kernel with PM_SUSPEND set and no PM_SLEEP,
we get a build warning in the xhci-plat driver about unused
functions.

To fix this, use "#ifdef CONFIG_PM_SLEEP", like we do in most
other drivers nowadays.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Mathias Nyman <mathias.nyman@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-plat.c

@@ -234,7 +234,7 @@ static int xhci_plat_remove(struct platform_device *dev)
 	return 0;
 }
 
-#ifdef CONFIG_PM
+#ifdef CONFIG_PM_SLEEP
 static int xhci_plat_suspend(struct device *dev)
 {
 	struct usb_hcd	*hcd = dev_get_drvdata(dev);