vfio/iommufd: Return errno in iommufd_cdev_attach_ioas_hwpt()

vfio/iommufd: Return errno in iommufd_cdev_attach_ioas_hwpt()

In preparation to implement auto domains have the attach function
return the errno it got during domain attach instead of a bool.

-EINVAL is tracked to track domain incompatibilities, and decide whether
to create a new IOMMU domain.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>