ARM: dts: uniphier: add dr_mode property to dwc3 node

Since commit 576e3cc700c5 ("usb: host: xhci-dwc3: Add dual role mode
support from DT"), warning is displayed if dr_mode is not specified.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/arch/arm/dts/uniphier-ld20.dtsi b/arch/arm/dts/uniphier-ld20.dtsi
index 927340f..44257af 100644
--- a/arch/arm/dts/uniphier-ld20.dtsi
+++ b/arch/arm/dts/uniphier-ld20.dtsi
@@ -426,6 +426,7 @@
 				compatible = "snps,dwc3";
 				reg = <0x65a00000 0x10000>;
 				interrupts = <0 134 4>;
+				dr_mode = "host";
 				tx-fifo-resize;
 			};
 		};