apm821xx: fix usb-otg on 4.14

Starting with 4.14, the "amcc,dwc-otg" needs to be used
in order to get the usb-otg to work.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/apm821xx/dts/apm82181.dtsi

@@ -248,7 +248,7 @@
 		};
 
 		USBOTG0: usbotg@bff80000 {
-			compatible = "amcc,usb-otg-405ex";
+			compatible = "amcc,dwc-otg";
 			reg = <4 0xbff80000 0x10000>;
 			interrupt-parent = <&USBOTG0>;
 			interrupts = <0 1 2>;