iommu/tegra-gart: Remove direct access of dev->iommu_fwspec

Use the accessor functions instead of directly dereferencing
dev->iommu_fwspec.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20200326150841.10083-5-joro@8bytes.org

drivers/iommu/tegra-gart.c

@@ -247,7 +247,7 @@ static int gart_iommu_add_device(struct device *dev)
 {
 	struct iommu_group *group;
 
-	if (!dev->iommu_fwspec)
+	if (!dev_iommu_fwspec_get(dev))
 		return -ENODEV;
 
 	group = iommu_group_get_for_dev(dev);