dt-bindings: rng: Drop unneeded quotes

Cleanup bindings dropping unneeded quotes. Once all these are fixed,
checking for this can be enabled in yamllint.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com> #brcm,iproc-rng200
Link: https://lore.kernel.org/r/20230327170153.4105594-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>