vfio-iommufd: Make vfio_iommufd_emulated_bind() return iommufd_access ID

vfio-iommufd: Make vfio_iommufd_emulated_bind() return iommufd_access ID

vfio device cdev needs to return iommufd_access ID to userspace if
bind_iommufd succeeds.

Link: https://lore.kernel.org/r/20230327093351.44505-5-yi.l.liu@intel.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Terrence Xu <terrence.xu@intel.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>