Fixes the following build error introduced by commit 3177bb76a8
("iommu/exynos: Implement DOMAIN_ATTR_GEOMETRY attribute"):
drivers/iommu/exynos-iommu.c: In function ‘exynos_iommu_domain_init’:
drivers/iommu/exynos-iommu.c:735:2: error: ‘dom’ undeclared
(first use in this function)