ARM: dts: gr8-evb: Fix RTC vendor

For some reason, the RTC vendor is reported to be phg, while the part is
actually made by the much more known NXP. Fix that.

Signed-off-by: Maxime Ripard <[e-mail]>

arch/arm/boot/dts/sun5i-gr8-evb.dts

···
 	};
 
 	pcf8563: rtc@51 {
-		compatible = "phg,pcf8563";
+		compatible = "nxp,pcf8563";
 		reg = <0x51>;
 	};
 };