vfio: check vfio_register_iommu_driver() return value

As vfio_register_iommu_driver() can fail, we should check the return value.

Signed-off-by: Bo Liu <liubo03@inspur.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/20220622045651.5416-1-liubo03@inspur.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>