dt-bindings: pinctrl: renesas: Drop unneeded quotes

Drop unneeded quotes over simple string values to fix a soon to be
enabled yamllint warning:

  [error] string value is redundantly quoted with any quotes (quoted-strings)

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20231122224409.2808999-1-robh@kernel.org


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>