dt-bindings: gpio: Correct indentation and style in DTS example

DTS example in the bindings should be indented with 2- or 4-spaces and
aligned with opening '- |', so correct any differences like 3-spaces or
mixtures 2- and 4-spaces in one binding.  While re-indenting, drop
unused labels.

No functional changes here, but saves some comments during reviews of
new patches built on existing code.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Sander Vanheule <sander@svanheule.net>
Reviewed-by: Manikandan Muralidharan <manikandan.m@microchip.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20250324125326.82270-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>