f2fs: flush data when enabling checkpoint back

During checkpoint=disable period, f2fs bypasses all the synchronous IOs such as
sync and fsync. So, when enabling it back, we must flush all of them in order
to keep the data persistent. Otherwise, suddern power-cut right after enabling
checkpoint will cause data loss.

Change-Id: I60dbaf9c720372c76f1c384446383dd8ff1ea4e9
Fixes: 4354994f ("f2fs: checkpoint disabling")
Cc: stable@vger.kernel.org
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Git-commit: 046c59c1
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git


Signed-off-by: Sayali Lokhande <quic_sayalil@quicinc.com>