iommufd: Add iommufd_ctx to iommufd_put_object()

Will be used in the next patch.

Link: https://lore.kernel.org/r/1-v2-ca9e00171c5b+123-iommufd_syz4_jgg@nvidia.com/


Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>