iommu/amd: Fix header file

Move function declaration inside AMD_IOMMU_H defination.

Fixes: fd5dff9d ("iommu/amd: Modify set_dte_entry() to use 256-bit DTE helpers")
Fixes: 457da576 ("iommu/amd: Lock DTE before updating the entry with WRITE_ONCE()")
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20250227162320.5805-6-vasant.hegde@amd.com


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