ARM: dts: r8a7779, marzen: Fix DU clock names

"make dtbs_check" complains:

    arch/arm/boot/dts/r8a7779-marzen.dt.yaml: display@fff80000: clock-names:0: 'du.0' was expected

Change the first clock name to match the DT bindings.
This has no effect on actual operation, as the Display Unit driver in
Linux does not use the first clock name on R-Car H1, but just grabs the
first clock.

Fixes: 665d79aa ("ARM: shmobile: marzen: Add DU external pixel clock to DT")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/9d5e1b371121883b3b3e10a3df43802a29c6a9da.1619699965.git.geert+renesas@glider.be

arch/arm/boot/dts/r8a7779-marzen.dts

@@ -145,7 +145,7 @@ &du {
 	status = "okay";
 
 	clocks = <&mstp1_clks R8A7779_CLK_DU>, <&x3_clk>;
-	clock-names = "du", "dclkin.0";
+	clock-names = "du.0", "dclkin.0";
 
 	ports {
 		port@0 {

arch/arm/boot/dts/r8a7779.dtsi

@@ -463,6 +463,7 @@ du: display@fff80000 {
 		reg = <0xfff80000 0x40000>;
 		interrupts = <GIC_SPI 31 IRQ_TYPE_LEVEL_HIGH>;
 		clocks = <&mstp1_clks R8A7779_CLK_DU>;
+		clock-names = "du.0";
 		power-domains = <&sysc R8A7779_PD_ALWAYS_ON>;
 		status = "disabled";