iommu/exynos: Fix build error

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)

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>