arm64: dts: socfpga: stratix10: add clock-names to DWC2 USB

The DWC2 USB bindings require clock-names property, to provide such to
fix warnings like:

  socfpga_stratix10_swvp.dtb: usb@ffb40000: 'clock-names' is a required property
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>

arch/arm64/boot/dts/altera/socfpga_stratix10.dtsi

@@ -510,6 +510,7 @@ usb1: usb@ffb40000 {
 			resets = <&rst USB1_RESET>, <&rst USB1_OCP_RESET>;
 			reset-names = "dwc2", "dwc2-ecc";
 			clocks = <&clkmgr STRATIX10_USB_CLK>;
+			clock-names = "otg";
 			iommus = <&smmu 7>;
 			status = "disabled";
 		};