[PATCH] libertas: don't tear down netdev in libertas_activate_card

libertas_activate_card() doesn't create the netdev, and shouldn't
free it on error.  The caller of libertas_activate_card() is
responsible for cleaning up errors from libertas_add_card(),
not libertas_activate_card().

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>