iommu/exynos-iommu: Set release_domain to exynos_identity_domain

iommu/exynos-iommu: Set release_domain to exynos_identity_domain

Following a coming core change to pass in the old domain pointer into the
attach_dev op and its callbacks, exynos_iommu_identity_attach() will need
this new argument too, which the release_device op doesn't provide.

Instead, the core provides a release_domain to attach to the device prior
to invoking the release_device callback. Thus, simply use that.

Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>