Use DBblock_REF instead of calcBLOCKBlockRef(getOwnNodeId()) as they are the same and the former is more efficient.

Makes it easier to grep for senders of signals to specific blocks


ndb/src/kernel/blocks/dblqh/DblqhMain.cpp:
  Use DBblock_REF instead of calcBLOCKBlockRef(getOwnNodeId()) as they are the same and the former is more efficient.