hw/i386/amd_iommu: Remove unused and wrongly set ats_enabled field

hw/i386/amd_iommu: Remove unused and wrongly set ats_enabled field

The ats_enabled field is set using HTTUNEN, which is wrong.
Fix this by removing the field as it is never used.

MST: includes a tweak suggested by Philippe

Fixes: d29a09ca68428 ("hw/i386: Introduce AMD IOMMU")
Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Message-Id: <20250801060507.3382-3-sarunkod@amd.com>
Message-ID: <948a6ac3-ded9-475b-8c45-9d36220b442b@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>