iommu/dma: Use helper functions to access dev->iommu_fwspec

Use the new helpers dev_iommu_fwspec_get()/set() to access
the dev->iommu_fwspec pointer. This makes it easier to move
that pointer later into another struct.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/dma-iommu.c

@@ -177,7 +177,7 @@ EXPORT_SYMBOL(iommu_put_dma_cookie);
 void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list)
 {
 
-	if (!is_of_node(dev->iommu_fwspec->iommu_fwnode))
+	if (!is_of_node(dev_iommu_fwspec_get(dev)->iommu_fwnode))
 		iort_iommu_msi_get_resv_regions(dev, list);
 
 }