drm: fix page_flip error handling

Free event and restore event_space only when page_flip->flags has
DRM_MODE_PAGE_FLIP_EVENT if page_flip() is failed.
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -3335,11 +3335,13 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 
 	ret = crtc->funcs->page_flip(crtc, fb, e);
 	if (ret) {
+		if (page_flip->flags & DRM_MODE_PAGE_FLIP_EVENT) {
 			spin_lock_irqsave(&dev->event_lock, flags);
 			file_priv->event_space += sizeof e->event;
 			spin_unlock_irqrestore(&dev->event_lock, flags);
 			kfree(e);
 		}
+	}
 
 out:
 	mutex_unlock(&dev->mode_config.mutex);