cinterion: fix 'ds' setting in CNMI command builder

Reported-by: Colin Helliwell <colin.helliwell@ln-systems.com>
diff --git a/plugins/cinterion/mm-broadband-modem-cinterion.c b/plugins/cinterion/mm-broadband-modem-cinterion.c
index 874d7fa..e82f78a 100644
--- a/plugins/cinterion/mm-broadband-modem-cinterion.c
+++ b/plugins/cinterion/mm-broadband-modem-cinterion.c
@@ -212,7 +212,7 @@
     if (!error) {
         if (value_supported (self->priv->cnmi_supported_ds, 2))
             g_string_append_printf (cmd, "%u,", 2);
-        if (value_supported (self->priv->cnmi_supported_ds, 1))
+        else if (value_supported (self->priv->cnmi_supported_ds, 1))
             g_string_append_printf (cmd, "%u,", 1);
         else if (value_supported (self->priv->cnmi_supported_ds, 0))
             g_string_append_printf (cmd, "%u,", 0);