iommu/vt-d: Remove VMD child device sanity check

Remove the sanity check required for VMD child devices.  The new
pci_real_dma_dev() DMA alias mechanism places them in the same IOMMU group
as the VMD endpoint.  Assignment of the group would require assigning the
VMD endpoint, where unbinding the VMD endpoint removes the child device
domain from the hierarchy.

Link: https://lore.kernel.org/r/1579613871-301529-6-git-send-email-jonathan.derrick@intel.com


Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>