ARM: shmobile: r8a7779 dtsi: Add SoC-specific thermal compatible property

The thermal node used the generic compatible property only.
Add the SoC-specific one, to make it future proof.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7779.dtsi

@@ -256,7 +256,7 @@ pfc: pfc@fffc0000 {
 	};
 
 	thermal@ffc48000 {
-		compatible = "renesas,rcar-thermal";
+		compatible = "renesas,thermal-r8a7779", "renesas,rcar-thermal";
 		reg = <0xffc48000 0x38>;
 	};