vfio: Stop using iommu_present()

IOMMU groups have been mandatory for some time now, so a device without
one is necessarily a device without any usable IOMMU, therefore the
iommu_present() check is redundant (or at best unhelpful).
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/537103bbd7246574f37f2c88704d7824a3a889f2.1649160714.git.robin.murphy@arm.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio.c

@@ -745,11 +745,11 @@ static struct vfio_group *vfio_group_find_or_alloc(struct device *dev)
 
 	iommu_group = iommu_group_get(dev);
 #ifdef CONFIG_VFIO_NOIOMMU
-	if (!iommu_group && noiommu && !iommu_present(dev->bus)) {
+	if (!iommu_group && noiommu) {
 		/*
 		 * With noiommu enabled, create an IOMMU group for devices that
-		 * don't already have one and don't have an iommu_ops on their
-		 * bus.  Taint the kernel because we're about to give a DMA
+		 * don't already have one, implying no IOMMU hardware/driver
+		 * exists.  Taint the kernel because we're about to give a DMA
 		 * capable device to a user without IOMMU protection.
 		 */
 		group = vfio_noiommu_group_alloc(dev, VFIO_NO_IOMMU);