usb: eth: Stop freeing the dev_data pointer.

It's never set to anything, so there's no reason to free it.

Change-Id: I140b7018b34ac081a20280fba1e24e8034552265
diff --git a/src/drivers/net/usb_eth.c b/src/drivers/net/usb_eth.c
index bf4588a..81aee73 100644
--- a/src/drivers/net/usb_eth.c
+++ b/src/drivers/net/usb_eth.c
@@ -113,7 +113,6 @@
 static void usb_eth_remove(GenericUsbDevice *dev)
 {
 	net_remove_device(usb_eth_net_device);
-	free(dev->dev_data);
 }
 
 static GenericUsbDriver usb_eth_driver = {