ARM: dts: r8a7745: Convert to new DU DT bindings

The DU DT bindings have been updated to drop the reg-names property.
Update the r8a7745 device tree accordingly.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20200218132217.21454-1-geert+renesas@glider.be

arch/arm/boot/dts/r8a7745.dtsi

@@ -1506,7 +1506,6 @@ vsp@fe930000 {
 		du: display@feb00000 {
 			compatible = "renesas,du-r8a7745";
 			reg = <0 0xfeb00000 0 0x40000>;
-			reg-names = "du";
 			interrupts = <GIC_SPI 256 IRQ_TYPE_LEVEL_HIGH>,
 				     <GIC_SPI 268 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&cpg CPG_MOD 724>, <&cpg CPG_MOD 723>;