amd_iommu_init: remove __init from amd_iommu_erratum_746_workaround

commit 318fe782 ("IOMMU, AMD Family15h Model10-1Fh erratum 746 Workaround")
added amd_iommu_erratum_746_workaround and it's marked as __init, which is wrong

WARNING: drivers/iommu/built-in.o(.text+0x639c): Section mismatch in reference from the function iommu_init_pci() to the function .init.text:amd_iommu_erratum_746_workaround()
The function iommu_init_pci() references
the function __init amd_iommu_erratum_746_workaround().
This is often because iommu_init_pci lacks a __init
annotation or the annotation of amd_iommu_erratum_746_workaround is wrong.

Signed-off-by: Nikola Pajkovsky <npajkovs@redhat.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>