dt-bindings: mfd: mediatek: mt6397: Add missing MT6331 regulator compat

Add the missing mediatek,mt6331-regulator in the compatible string
list for the regulators subnode.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260113110000.36953-3-angelogioacchino.delregno@collabora.com
Signed-off-by: Lee Jones <lee@kernel.org>

Author: AngeloGioacchino Del Regno

Documentation/devicetree/bindings/mfd/mediatek,mt6397.yaml

@@ -90,6 +90,7 @@ properties:
           - enum:
               - mediatek,mt6323-regulator
               - mediatek,mt6328-regulator
+              - mediatek,mt6331-regulator
               - mediatek,mt6358-regulator
               - mediatek,mt6359-regulator
               - mediatek,mt6397-regulator