VT-d: skip IOMMU bitmap cleanup for phantom devices

VT-d: skip IOMMU bitmap cleanup for phantom devices

Doing the cleanup also for phantom devices is at best redundant with
doing it for the corresponding real device. I couldn't force myself into
checking all the code paths whether it really is: It seems better to
explicitly skip this step in such cases.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>