ARM: at91/dt: sama5d4: change watchdog compatible

Change the watchdog compatible to "atmel,sama5d4-wdt" to support
SAMA5D4 watchdog driver.
Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/sama5d4.dtsi

@@ -1300,7 +1300,7 @@ pit: timer@fc068630 {
 			};
 
 			watchdog@fc068640 {
-				compatible = "atmel,at91sam9260-wdt";
+				compatible = "atmel,sama5d4-wdt";
 				reg = <0xfc068640 0x10>;
 				clocks = <&clk32k>;
 				status = "disabled";