AMD IOMMU: correctly propagate errors from amd_iommu_init()

AMD IOMMU: correctly propagate errors from amd_iommu_init()

... instead of using -ENODEV for any kind of error. It in particular
addresses Coverity ID 1362694 (introduced by commit eb48587210 ["AMD
IOMMU: introduce support for IVHD block type 11h"]).

Coverity ID: 1362694

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>