nimble/host: Fix cleaning conn when sync transfer enabled

When host is waiting for the sync transfer, conn->psync is allocated.
If ACL disconnection happen before sync is established, make sure to
free it.

nimble/host/src/ble_hs_atomic.c

@@ -28,6 +28,11 @@ ble_hs_atomic_conn_delete(uint16_t conn_handle)
     conn = ble_hs_conn_find(conn_handle);
     if (conn != NULL) {
         ble_hs_conn_remove(conn);
+#if MYNEWT_VAL(BLE_PERIODIC_ADV_SYNC_TRANSFER)
+        if (conn->psync) {
+            ble_hs_periodic_sync_free(conn->psync);
+        }
+#endif
         ble_hs_conn_free(conn);
 
     }