dt-bindings: interrupt-controller: mediatek,mt6577-sysirq: Drop unnecessary quotes

Drop unnecessary quotes which aren't needed in yaml. This is checked by
yamllint, but this case was excluded due to the comma and yamllint's
mishandling of some cases with commas. That's now fixed in yamllint
1.34.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20240426195404.2771046-1-robh@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>