dbus: Add missing signal description for WPS (7)

Commit caff399250311abfea3376b38530a88bb78b957d added a property named
"WPS" to the dbus interface. It did not add the new
WPAS_DBUS_BSS_PROP_WPS property to the function responsible for marking
changed properties though. This cause the following messages to be
printed repeatedly to syslog:

    dbus: wpas_dbus_bss_signal_prop_changed: Unknown Property value 7

Signed-hostap: Peter Wu <lekensteyn@gmail.com>

wpa_supplicant/dbus/dbus_new.c

@@ -1808,6 +1808,9 @@ void wpas_dbus_bss_signal_prop_changed(struct wpa_supplicant *wpa_s,
 	case WPAS_DBUS_BSS_PROP_RSN:
 		prop = "RSN";
 		break;
+	case WPAS_DBUS_BSS_PROP_WPS:
+		prop = "WPS";
+		break;
 	case WPAS_DBUS_BSS_PROP_IES:
 		prop = "IEs";
 		break;