ramips: don't enable usb for the WT3020-4M

That device does not have a USB port. It as the same board as the
WT3020-8M, but without soldered USB port port. Also the case lacks the
opening for the port.

Reported-by: Alberto Bursi <alberto.bursi@outlook.it>
Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/ramips/dts/WT3020-8M.dts

@@ -7,6 +7,14 @@
 	model = "Nexx WT3020 (8M)";
 };
 
+&ehci {
+	status = "okay";
+};
+
+&ohci {
+	status = "okay";
+};
+
 &spi0 {
 	status = "okay";
 

target/linux/ramips/dts/WT3020.dtsi

@@ -37,15 +37,6 @@
 	status = "okay";
 };
 
-
-&ehci {
-	status = "okay";
-};
-
-&ohci {
-	status = "okay";
-};
-
 &ethernet {
 	mtd-mac-address = <&factory 0x4>;
 	mediatek,portmap = "wllll";