dt-bindings: connector: usb: align example indentation to four-space

One DTS example was using 8-space indentation, while others 2-space.
For complex DTS with multiple levels, 2-space is not that readable and
in DTS examples 4-space is preferred.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220624162141.25890-1-krzysztof.kozlowski@linaro.org