Met the following compiler warning message:
>[38/80] Building CXX object
src/librbd/CMakeFiles/librbd_plugin_pwl_cache.dir/cache/pwl/ssd/WriteLog.cc.o
>../src/librbd/cache/pwl/ssd/WriteLog.cc:37:25: warning: unused variable
'ops_appended_together' [-Wunused-const-variable]
>const unsigned long int ops_appended_together = MAX_WRITES_PER_SYNC_POINT;
Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>