CVE-2026-53280: iommu: Fix NULL group->domain dereference in pci_dev_reset_iommu_done()

In the Linux kernel, the following vulnerability has been resolved:

iommu: Fix NULL group->domain dereference in pcidevresetiommudone()

Local sashiko review pointed it out that group->domain could be NULL when a default domain fails to allocate during the first probe, which can crash at domain->ops->attachdev dereference in iommuattachdevice() invoked by pcidevresetiommudone().

pcidevresetiommuprepare() is fine as an olddomain pointer can be NULL.

Skip the re-attach in pcidevresetiommudone() to fix the bug.