Fix Coverity Scan CID 21911 (Using uninitialized value data_req. Field...

Fix Coverity Scan CID 21911 (Using uninitialized value data_req. Field data_req.buffer_occupancy_in_pdus is uninitialized.)

openair2/LAYER2/RLC/AM_v9.3.0/rlc_am.c

@@ -811,6 +811,7 @@ rlc_am_mac_data_request (
       tb_p = tb_p->next;
     } /* while */
   } /* MESSAGE_CHART_GENERATOR && data_req.data.nb_elements > 0 */
+  data_req.buffer_occupancy_in_pdus = 0;
 
   return data_req;
 }