xfs: always init fdblocks in mount

hulk inclusion
category: bugfix
bugzilla: 31088
CVE: NA

---------------------------

Use fuzz(hydra) to test XFS and automatically generate
tmp.img(XFS v5 format, but some metadata is wrong)

xfs_repair information(just one AG):
agf_freeblks 0, counted 3224 in ag 0
agf_longest 0, counted 3224 in ag 0
sb_fdblocks 3228, counted 3224

Test as follows:
mount tmp.img tmpdir
cp file1M tmpdir
sync

In 4.19-stable, sync will stuck, while in linux-next, sync not stuck.
The reason is same to commit d0c7feaf
("xfs: add agf freeblocks verify in xfs_agf_verify"), cause agf_longest
is 0, we can not block this in xfs_agf_verify.

Make sure fdblocks is always inited in mount(also init ifree, icount).

xfs_mountfs
  xfs_check_summary_counts
    xfs_initialize_perag_data

Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>