drm: rcar-du: fix warnings

drivers/gpu/drm/rcar-du/rcar_du_drv.c:190:5: warning: "CONFIG_PM_SLEEP" is not defined [-Wundef]

Always use #ifdef with CONFIG symbols, never just bare #if
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/rcar-du/rcar_du_drv.c

@@ -187,7 +187,7 @@ static struct drm_driver rcar_du_driver = {
  * Power management
  */
 
-#if CONFIG_PM_SLEEP
+#ifdef CONFIG_PM_SLEEP
 static int rcar_du_pm_suspend(struct device *dev)
 {
 	struct rcar_du_device *rcdu = dev_get_drvdata(dev);