arm64: dts: r8a7795: Use USB3.0 fallback compatibility string

Use recently added fallback compatibility string in r8a7795 device tree.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>

arch/arm64/boot/dts/renesas/r8a7795.dtsi

@@ -982,7 +982,7 @@ sata: sata@ee300000 {
 		};
 
 		xhci0: usb@ee000000 {
-			compatible = "renesas,xhci-r8a7795";
+			compatible = "renesas,xhci-r8a7795", "renesas,rcar-gen3-xhci";
 			reg = <0 0xee000000 0 0xc00>;
 			interrupts = <GIC_SPI 102 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&cpg CPG_MOD 328>;
@@ -991,7 +991,7 @@ xhci0: usb@ee000000 {
 		};
 
 		xhci1: usb@ee0400000 {
-			compatible = "renesas,xhci-r8a7795";
+			compatible = "renesas,xhci-r8a7795", "renesas,rcar-gen3-xhci";
 			reg = <0 0xee040000 0 0xc00>;
 			interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&cpg CPG_MOD 327>;