Remove unused function warning in WPS NFC case

When I use CONFIG_WPS_NFC=y a warning appears.

wps_supplicant.c:1872:12: warning: 'wpas_wps_add_nfc_password_token'
defined but not used [-Wunused-function]

This patch removes this warning.

Signed-hostap: Masashi Honma <masashi.honma at gmail.com>

wpa_supplicant/wps_supplicant.c

@@ -1869,6 +1869,7 @@ static int wpas_wps_use_cred(struct wpa_supplicant *wpa_s,
 }
 
 
+#ifdef CONFIG_WPS_ER
 static int wpas_wps_add_nfc_password_token(struct wpa_supplicant *wpa_s,
 					   struct wps_parse_attr *attr)
 {
@@ -1876,6 +1877,7 @@ static int wpas_wps_add_nfc_password_token(struct wpa_supplicant *wpa_s,
 		wpa_s->wps->registrar, attr->oob_dev_password,
 		attr->oob_dev_password_len);
 }
+#endif /* CONFIG_WPS_ER */
 
 
 static int wpas_wps_nfc_tag_process(struct wpa_supplicant *wpa_s,