hw/arm/virt: Fix devicetree warning about the SMMU node

The SMMUv3 node isn't expected to have clock properties
(unlike the SMMUv2). Fix the corresponding dt-validate warning:

  smmuv3@9050000: 'clock-names', 'clocks' do not match any of the regexes: 'pinctrl-[0-9]+'
  From schema: linux/Documentation/devicetree/bindings/iommu/arm,smmu-v3.yaml

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: tweaked commit message as suggested by Eric]
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20220927100347.176606-7-jean-philippe@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>