ARM: dts: at91: sama5d4: use correct rtc compatible

Use the sama5d4 specific compatible string for the RTC.

Link: https://lore.kernel.org/r/20191229204421.337612-9-alexandre.belloni@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

arch/arm/boot/dts/sama5d4.dtsi

@@ -884,7 +884,7 @@ clk32k: sckc@fc068650 {
 			};
 
 			rtc@fc0686b0 {
-				compatible = "atmel,at91rm9200-rtc";
+				compatible = "atmel,sama5d4-rtc";
 				reg = <0xfc0686b0 0x30>;
 				interrupts = <1 IRQ_TYPE_LEVEL_HIGH 7>;
 				clocks = <&clk32k>;