staging: ath6kl: use free_netdev(netdev) instead of kfree()

It is not guaranteed that free_netdev() is macro.
Freeing netdev without free_netdev() leads to net, tx leaks.
I might lead to dereferencing freed pointer.

Signed-off-by: Vasiliy Kulikov <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/ath6kl/os/linux/ar6000_drv.c

···
         unregister_netdev(dev);
         is_netdev_registered = 0;
     }
-#ifndef free_netdev
-    kfree(dev);
-#else
     free_netdev(dev);
-#endif
 
 #ifdef ATH6K_CONFIG_CFG80211
     ar6k_cfg80211_deinit(ar);
···
         ar6000_stop_ap_interface(ar);
 
         unregister_netdev(arApNetDev);
-#ifndef free_netdev
-        kfree(arApNetDev);
-#else
         free_netdev(apApNetDev);
-#endif
 
         A_PRINTF("Remove AP interface\n");
     }