dt-bindings: mfd: Add compatible for MT6331 PMIC

Add a compatible for the MT6331 PMIC MFD device.
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220520124039.228314-5-angelogioacchino.delregno@collabora.com

Documentation/devicetree/bindings/mfd/mt6397.txt

@@ -20,6 +20,7 @@ This document describes the binding for MFD device and its sub module.
 Required properties:
 compatible:
 	"mediatek,mt6323" for PMIC MT6323
+	"mediatek,mt6331" for PMIC MT6331 and MT6332
 	"mediatek,mt6358" for PMIC MT6358 and MT6366
 	"mediatek,mt6359" for PMIC MT6359
 	"mediatek,mt6397" for PMIC MT6397