hw/i386/amd_iommu: Explicit use of AMDVI_BASE_ADDR in amdvi_init

hw/i386/amd_iommu: Explicit use of AMDVI_BASE_ADDR in amdvi_init

By accessing MemoryRegion internals, amdvi_init() gives the false
idea that the PCI BAR can be modified. However this isn't true
(at least the model isn't ready for that): the device is explicitly
maps at the BAR at the fixed AMDVI_BASE_ADDR address in
amdvi_sysbus_realize(). Since the SysBus API isn't designed to
remap regions, directly use the fixed address in amdvi_init().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230313153031.86107-3-philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 6291a28645a0656477bc5962a81b181e6a99487c)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>