drm/rockchip: don't leak iommu mapping

arm_iommu_attach_device() takes its own reference to the mapping we give
it.  Since we do not keep a reference to the mapping ourselves, we must
release it before returning.

Also fix the error path, which fails to release the mapping if it has
called arm_iommu_detach_device() since that clears archdata.mapping.
Signed-off-by: John Keeping <john@metanate.com>

drivers/gpu/drm/rockchip/rockchip_drm_drv.c

@@ -218,6 +218,7 @@ static int rockchip_drm_load(struct drm_device *drm_dev, unsigned long flags)
 	if (ret)
 		goto err_vblank_cleanup;
 
+	arm_iommu_release_mapping(mapping);
 	return 0;
 err_vblank_cleanup:
 	drm_vblank_cleanup(drm_dev);
@@ -228,7 +229,7 @@ static int rockchip_drm_load(struct drm_device *drm_dev, unsigned long flags)
 err_detach_device:
 	arm_iommu_detach_device(dev);
 err_release_mapping:
-	arm_iommu_release_mapping(dev->archdata.mapping);
+	arm_iommu_release_mapping(mapping);
 err_config_cleanup:
 	drm_mode_config_cleanup(drm_dev);
 	drm_dev->dev_private = NULL;