iommu/amd: Remove unused variable

Remove 'amd_iommu_aperture_order' as its not used since commit d9cfed92.

Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20250227162320.5805-3-vasant.hegde@amd.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>