libertas: fix memory corruption in lbs_remove_card()

"priv" is stored at the end of the wiphy structure, which is freed
during the call to lbs_cfg_free(). It must not be touched afterwards.

Remove the unnecessary NULL assignment causing this memory corruption.
Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/main.c

@@ -915,8 +915,6 @@ void lbs_remove_card(struct lbs_private *priv)
 
 	lbs_free_adapter(priv);
 	lbs_cfg_free(priv);
-
-	priv->dev = NULL;
 	free_netdev(dev);
 
 	lbs_deb_leave(LBS_DEB_MAIN);