iommu/amd: Fix hotplug with iommu=pt

commit 2c9195e9 upstream.

This did not work because devices are not put into the
pt_domain. Fix this.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>