L2CAP COC example : Fixed freeing up of same memory address twice.

examples/bluetooth/nimble/ble_l2cap_coc/coc_blecent/main/main.c

@@ -59,7 +59,6 @@ blecent_l2cap_coc_send_data(struct ble_l2cap_chan *chan)
     } else {
         MODLOG_DFLT(INFO,"Data sending failed, rc = %d",rc);
     }
-    os_mbuf_free(sdu_rx_data);
 }
 
 /**