usb: Return -ENOENT when no devices are found

When USB finds no devices it currently returns -EPERM which bootstd does
not understand. This causes other bootdevs of the same priority to be
skipped.

Fix this by returning the correct error code.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/usb/host/usb-uclass.c b/drivers/usb/host/usb-uclass.c
index 02c0138..7a03435 100644
--- a/drivers/usb/host/usb-uclass.c
+++ b/drivers/usb/host/usb-uclass.c
@@ -346,7 +346,7 @@
 	if (controllers_initialized == 0)
 		printf("No working controllers found\n");
 
-	return usb_started ? 0 : -1;
+	return usb_started ? 0 : -ENOENT;
 }
 
 int usb_setup_ehci_gadget(struct ehci_ctrl **ctlrp)