WPS: Fix unused variable warning

The wpa_supplicant compilation without CONFIG_WPS option results in
messages below.

scan.c: In function 'wpa_supplicant_scan':
scan.c:246: warning: unused variable 'wps'

This trivial patch erases this warning.

wpa_supplicant/scan.c

@@ -243,8 +243,8 @@ static void wpa_supplicant_scan(void *eloop_ctx, void *timeout_ctx)
 	struct wpa_ssid *ssid;
 	int scan_req = 0, ret;
 	struct wpabuf *wps_ie = NULL;
-	int wps = 0;
 #ifdef CONFIG_WPS
+	int wps = 0;
 	enum wps_request_type req_type = WPS_REQ_ENROLLEE_INFO;
 #endif /* CONFIG_WPS */
 	struct wpa_driver_scan_params params;