libertas: remove double assignment of dev->netdev_ops

This came in through the patch titled:
    libertas: first stab at cfg80211 support

I only noticed it because it breaks compat-wireless :)

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Acked-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>