iommu/amd: Fix missing iommu_shutdown initialization in passthrough mode

iommu/amd: Fix missing iommu_shutdown initialization in passthrough mode

commit f2f12b6fc032c7b1419fd6db84e2868b5f05a878 upstream.

The iommu_shutdown callback is not initialized when the AMD
IOMMU driver runs in passthrough mode. Fix that by moving
the callback initialization before the check for
passthrough mode.

Signed-off-by: Shuah Khan <shuah.khan@hp.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>