arm: dts: renesas: r8a77980: Remove r8a77970 DU compatible

The r8a77970 was added with a compatible string for a different device
rather than adding the correct compatible to the driver.

Remove the unnecessary compatible which is for a different platform.
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Link: https://lore.kernel.org/r/20190912103734.1879-1-kieran.bingham+renesas@ideasonboard.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

arch/arm64/boot/dts/renesas/r8a77980.dtsi

@@ -1484,8 +1484,7 @@ csi41vin7: endpoint@3 {
 		};
 
 		du: display@feb00000 {
-			compatible = "renesas,du-r8a77980",
-				     "renesas,du-r8a77970";
+			compatible = "renesas,du-r8a77980";
 			reg = <0 0xfeb00000 0 0x80000>;
 			interrupts = <GIC_SPI 256 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&cpg CPG_MOD 724>;