dm: usb: Add an errno.h header to usb_ether.c

This is required on some platforms, so add it.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/usb/eth/usb_ether.c

@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <errno.h>
 #include <malloc.h>
 #include <usb.h>
 #include <dm/device-internal.h>