broadband-modem: normalize also operator code

The operator code (MCCMNC) may also be given encoded in the current
charset (e.g. UCS2).

Based on a patch from Colin Helliwell <colin.helliwell@ln-systems.com>

plugins/altair/mm-broadband-modem-altair-lte.c

@@ -1128,7 +1128,7 @@ modem_3gpp_load_operator_name_finish (MMIfaceModem3gpp *self,
                                            error))
         return NULL;
 
-    mm_3gpp_normalize_operator_name (&operator_name, MM_MODEM_CHARSET_UNKNOWN);
+    mm_3gpp_normalize_operator (&operator_name, MM_MODEM_CHARSET_UNKNOWN);
     if (operator_name)
         mm_dbg ("loaded Operator Name: %s", operator_name);
     return operator_name;