dt-bindings: mfd: mediatek: Update RTC to include MT6323

Add MT6323 to RTC bindings.
Signed-off-by: Josef Friedl <josef.friedl@speed.at>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/mt6397.txt

@@ -22,8 +22,10 @@ compatible: "mediatek,mt6397" or "mediatek,mt6323"
 Optional subnodes:
 
 - rtc
-	Required properties:
+	Required properties: Should be one of follows
+		- compatible: "mediatek,mt6323-rtc"
 		- compatible: "mediatek,mt6397-rtc"
+	For details, see ../rtc/rtc-mt6397.txt
 - regulators
 	Required properties:
 		- compatible: "mediatek,mt6397-regulator"