broadband-modem-qmi: fix radio interface variable name

Sync with libqmi:

commit ebfa80154fad012bb6ea3e964dcea6f5b6cf3f91
Author: Aleksander Morgado <aleksander@lanedo.com>
Date:   Thu Aug 2 12:06:09 2012 +0200

    nas: consolidate variable names for `QmiNasRadioInterface' types

src/mm-broadband-modem-qmi.c

@@ -2578,7 +2578,7 @@ get_3gpp_access_technology (GArray *array,
         if (element->mcc == mcc &&
             element->mnc == mnc) {
             array_used_flags[i] = TRUE;
-            return access_technology_from_qmi_rat (element->rat);
+            return access_technology_from_qmi_rat (element->radio_interface);
         }
     }