arm/smmuv3: Fix missing VMSD terminator

The 'vmstate_smmuv3_queue' is missing the end-of-list marker.

Fixes: 10a83cb9
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-id: 20180727135406.15132-1-dgilbert@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: dropped stray blank line]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>