Don't need to collect dirty sit entries and flush sit journal to sit
entries when there's no dirty sit entries. This patch check dirty_sentries
earlier just like flush_nat_entries.
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> Reviewed-by: Chao Yu <chao2.yu@samsung.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>