amd_iommu: Rename variable mmio to mr_mmio

amd_iommu: Rename variable mmio to mr_mmio

Rename the MMIO memory region variable 'mmio' to 'mr_mmio'
so to correctly name align with struct AMDVIState::variable type.

No functional change intended.

Reviewed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Santosh Shukla <santosh.shukla@amd.com>
Message-Id: <20240927172913.121477-2-santosh.shukla@amd.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>