Staging: vt6656: problems in error handling

The first kfree(pDevice) is pointless because pDevice is NULL.  The
second kfree(pDevice) is a double free because pDevice is the driver's
private data and that is already freed by free_netdev(netdev).  Also the
free_netdev() error path doesn't call usb_put_dev().

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>