dt-bindings: arm-smmu: Fix json-schema syntax

dt-bindings: arm-smmu: Fix json-schema syntax

Commit 8485fbaf8127 ("dt-bindings: arm-smmu: Add Tegra186 compatible
string") introduced a jsonschema syntax error as a result of a rebase
gone wrong. Fix it.

Fixes: 8485fbaf8127 ("dt-bindings: arm-smmu: Add Tegra186 compatible string")
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210621140036.2879563-1-thierry.reding@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>