Staging: vt6655-6: potential NULL dereference in hostap_disable_hostapd()

We fixed this to use free_netdev() instead of kfree() but unfortunately
free_netdev() doesn't accept NULL pointers.  Smatch complains about
this, it's not something I discovered through testing.

Fixes: 3030d40b ('staging: vt6655: use free_netdev instead of kfree')
Fixes: 0a438d5b ('staging: vt6656: use free_netdev instead of kfree')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>