dt-binding: mediatek: mt8192: update mtk-wdt document

update mtk-wdt document for MT8192 platform
Signed-off-by: Crystal Guo <crystal.guo@mediatek.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20201014131936.20584-3-crystal.guo@mediatek.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/mtk-wdt.txt

@@ -12,6 +12,7 @@ Required properties:
 	"mediatek,mt7629-wdt", "mediatek,mt6589-wdt": for MT7629
 	"mediatek,mt8183-wdt": for MT8183
 	"mediatek,mt8516-wdt", "mediatek,mt6589-wdt": for MT8516
+	"mediatek,mt8192-wdt": for MT8192
 
 - reg : Specifies base physical address and size of the registers.