net: lwip: do_ping() should return CMD_RET_FAILURE when no device

do_ping() expects ping_loop() to return a negative value on error, so
that it can propagate it to the caller as CMD_RET_FAILURE. This is not
the case when no ethernet device is found, so fix that.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

net/lwip/ping.c

@@ -121,7 +121,7 @@ static int ping_loop(struct udevice *udev, const ip_addr_t *addr)
 
 	netif = net_lwip_new_netif(udev);
 	if (!netif)
-		return CMD_RET_FAILURE;
+		return -ENODEV;
 
 	printf("Using %s device\n", udev->name);