vfio: Use config not menuconfig for VFIO_NOIOMMU

VFIO_NOIOMMU is supposed to be an element in the VFIO menu, not start
a new menu. Correct this copy-paste mistake.

Fixes: 03a76b60

 ("vfio: Include No-IOMMU mode")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/0-v1-3f0b685c3679+478-vfio_menuconfig_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>