drm/exynos: fix to detach device of iommu

The arm_iommu_detach_device() is a function to detach device of iommu
attached by arm_iommu_attach_device(). The exynos-drm uses
arm_iommu_attach_device() so it should use arm_iommu_detach_device() to
detach device of iommu, not iommu_detach_device().

The drm_release_iommu_mapping() is a function to release mapping of
iommu created by arm_iommu_create_mapping(). It is called by
exynos_drm_unload() so shouldn't be called by drm_iommu_detach_device().
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_iommu.c

@@ -139,6 +139,5 @@ void drm_iommu_detach_device(struct drm_device *drm_dev,
 	if (!mapping || !mapping->domain)
 		return;
 
-	iommu_detach_device(mapping->domain, subdrv_dev);
-	drm_release_iommu_mapping(drm_dev);
+	arm_iommu_detach_device(subdrv_dev);
 }