FTL core poller should return SPDK_POLLER_BUSY flag only when some writes operations were processed. Signed-off-by: Wojciech Malikowski <wojciech.malikowski@intel.com> Change-Id: I50e2b536fbec819887148cc045d76c5c5d78beb2 Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/3619 Tested-by: SPDK CI Jenkins <sys_sgci@intel.com> Reviewed-by: Jim Harris <james.r.harris@intel.com> Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com> Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>