ARM: dts: r8a7791: Use renesas,rcar-gen2-usb-phy fallback binding

A fallback binding for the Renesas R-Car Gen2 PHY driver was
added by commit 7777cb8b ("phy: rcar-gen2: add fallback binding").
This patch makes use of this binding in the DT for the r8a7791 SoC.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

arch/arm/boot/dts/r8a7791.dtsi

@@ -934,7 +934,8 @@ hsusb: usb@e6590000 {
 	};
 
 	usbphy: usb-phy@e6590100 {
-		compatible = "renesas,usb-phy-r8a7791";
+		compatible = "renesas,usb-phy-r8a7791",
+			     "renesas,rcar-gen2-usb-phy";
 		reg = <0 0xe6590100 0 0x100>;
 		#address-cells = <1>;
 		#size-cells = <0>;