amd_iommu_is_attach_deferred() is a callback function called by
iommu_ops. Make it as static.

No functional changes intended.
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20240828111029.5429-3-vasant.hegde@amd.comSigned-off-by: Joerg Roedel <jroedel@suse.de>