databases/rocksdb: Fix build on i386

utilities/transactions/pessimistic_transaction.cc:691:25: error: implicit conversion from 'type' (aka 'unsigned long long') to 'size_t' (aka 'unsigned int') changes value from 18446744073709551615 to 4294967295 [-Werror,-Wconstant-conversion]

: std::numeric_limits<uint64_t>::max();
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

utilities/transactions/pessimistic_transaction.cc:766:23: error: implicit conversion from 'type' (aka 'unsigned long long') to 'size_t' (aka 'unsigned int') changes value from 18446744073709551615 to 4294967295 [-Werror,-Wconstant-conversion]

: std::numeric_limits<uint64_t>::max();
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

2 errors generated.