drm/nouveau: Fix error handling in nv50_disp_atomic_commit

Make it more clear that post commit return ret is really return 0,

and add a missing drm_atomic_helper_cleanup_planes when
drm_atomic_helper_wait_for_fences fails.

Fixes: 839ca903f12e ("drm/nouveau/kms/nv50: transition to atomic interfaces internally")
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.10+
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170711143314.2148-2-maarten.lankhorst@linux.intel.com
Reviewed-by: Sean Paul <seanpaul@chromium.org>
[mlankhorst: Use if (ret) to remove the goto in success case.]
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/nouveau/nv50_display.c

@@ -4120,7 +4120,7 @@ nv50_disp_atomic_commit(struct drm_device *dev,
 	if (!nonblock) {
 		ret = drm_atomic_helper_wait_for_fences(dev, state, true);
 		if (ret)
-			goto done;
+			goto err_cleanup;
 	}
 
 	for_each_plane_in_state(state, plane, plane_state, i) {
@@ -4148,7 +4148,7 @@ nv50_disp_atomic_commit(struct drm_device *dev,
 		if (crtc->state->enable) {
 			if (!drm->have_disp_power_ref) {
 				drm->have_disp_power_ref = true;
-				return ret;
+				return 0;
 			}
 			active = true;
 			break;
@@ -4160,6 +4160,9 @@ nv50_disp_atomic_commit(struct drm_device *dev,
 		drm->have_disp_power_ref = false;
 	}
 
+err_cleanup:
+	if (ret)
+		drm_atomic_helper_cleanup_planes(dev, state);
 done:
 	pm_runtime_put_autosuspend(dev->dev);
 	return ret;