Fix two small bugs:
    - For the I/O store, thread.store_ctr-- in ReadStage, and
    thread.store_ctr++ in MemoryStage. The store counter should not be
    decreased as there is no write completion for I/O store.
    - The thread.store_ctr will not be incremented if the write
    completion is called out of FT scope (i.e. family.ftmode=0).