iommu/tegra: gart: Don't detach devices from inactive domains

There could be unlimited number of allocated domains, but only one domain
can be active at a time. Hence devices must be detached only from the
active domain.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>