Use SARA-G3XX family macro

Author: Wajahat Abbas

features/cellular/framework/targets/UBLOX/AT/UBLOX_AT.cpp

@@ -104,7 +104,7 @@ nsapi_error_t UBLOX_AT::init()
 
     nsapi_error_t err = NSAPI_ERROR_OK;
 
-#ifdef UBX_MDM_SARA_G350
+#ifdef UBX_MDM_SARA_G3XX
     err = _at->at_cmd_discard("+CFUN", "=0");
 
     if (err == NSAPI_ERROR_OK) {