drm/radeon: Unreference GEM object outside of spinlock in page flip error path.

Should fix https://bugzilla.redhat.com/show_bug.cgi?id=726277 .
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_display.c

@@ -473,8 +473,8 @@ static int radeon_crtc_page_flip(struct drm_crtc *crtc,
 	spin_lock_irqsave(&dev->event_lock, flags);
 	radeon_crtc->unpin_work = NULL;
 unlock_free:
-	drm_gem_object_unreference_unlocked(old_radeon_fb->obj);
 	spin_unlock_irqrestore(&dev->event_lock, flags);
+	drm_gem_object_unreference_unlocked(old_radeon_fb->obj);
 	radeon_fence_unref(&work->fence);
 	kfree(work);