memory: Constify IOMMUTLBEvent in memory_region_notify_iommu_one()

@event access is read-only.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20240612132532.85928-2-philmd@linaro.org>
2 files changed