WPS: Fixed deinit code for freeing config and registrar data

WPS: Fixed deinit code for freeing config and registrar data

We need to be a bit more careful when removing the WPS configuration
block since wpa_s->current_ssid may still be pointing at it. In
addition, registrar pointer in wps_context will need to be cleared
since the context data is now maintained over multiple EAP-WSC runs.
Without this, certain WPS operations could have used freed memory.