hw/i386/amd_iommu.c: Fix corruption of log events passed to guest

hw/i386/amd_iommu.c: Fix corruption of log events passed to guest

In the function amdvi_log_event(), we write an event log buffer
entry into guest ram, whose contents are passed to the function
via the "uint64_t *evt" argument. Unfortunately, a spurious
'&' in the call to dma_memory_write() meant that instead of
writing the event to the guest we would write the literal value
of the pointer, plus whatever was in the following 8 bytes
on the stack. This error was spotted by Coverity.

Fix the bug by removing the '&'.

Fixes: CID 1421945
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200326105349.24588-1-peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>