dt-bindings: arm: psci: change labels to lower-case in example

DTS coding style expects labels to be lowercase, so adjust the example
code.  No functional impact.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20250501150934.77317-3-krzysztof.kozlowski@linaro.org


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