arm64: dts: mt6359: Add missing 'compatible' property to regulators node

arm64: dts: mt6359: Add missing 'compatible' property to regulators node

The 'compatible' property is required by the
'mfd/mediatek,mt6397.yaml' binding. Add it to fix the following
dtb-check error:
mediatek/mt8395-radxa-nio-12l.dtb: pmic: regulators:
'compatible' is a required property

Fixes: 3b7d143be4b7 ("arm64: dts: mt6359: add PMIC MT6359 related nodes")
Signed-off-by: Julien Massot <julien.massot@collabora.com>
Link: https://lore.kernel.org/r/20250505-mt8395-dtb-errors-v1-3-9c4714dcdcdb@collabora.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>