drm/stm: drv: fix suspend/resume

Without this fix, the system can not go in "suspend" mode
due to an error in drv_suspend function.

Fixes: 35ab6cfb ("drm/stm: support runtime power management")
Signed-off-by: Yannick Fertré <yannick.fertre@st.com>
Acked-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1560755897-5002-1-git-send-email-yannick.fertre@st.com

drivers/gpu/drm/stm/drv.c

@@ -136,8 +136,7 @@ static __maybe_unused int drv_suspend(struct device *dev)
 	struct ltdc_device *ldev = ddev->dev_private;
 	struct drm_atomic_state *state;
 
-	if (WARN_ON(!ldev->suspend_state))
-		return -ENOENT;
+	WARN_ON(ldev->suspend_state);
 
 	state = drm_atomic_helper_suspend(ddev);
 	if (IS_ERR(state))
@@ -155,15 +154,17 @@ static __maybe_unused int drv_resume(struct device *dev)
 	struct ltdc_device *ldev = ddev->dev_private;
 	int ret;
 
+	if (WARN_ON(!ldev->suspend_state))
+		return -ENOENT;
+
 	pm_runtime_force_resume(dev);
 	ret = drm_atomic_helper_resume(ddev, ldev->suspend_state);
-	if (ret) {
+	if (ret)
 		pm_runtime_force_suspend(dev);
-		ldev->suspend_state = NULL;
-		return ret;
-	}
 
-	return 0;
+	ldev->suspend_state = NULL;
+
+	return ret;
 }
 
 static __maybe_unused int drv_runtime_suspend(struct device *dev)