staging: vt6655: return ENOMEM rather than ENODEV when alloc_etherdev fail

when alloc_etherdev fails we should be returning ENOMEM, not ENODEV

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>