ext4: use proper csum calculation in ext4_rename

In ext4_rename, when the old name is a dir, we need to
change ".." to its new parent and journal the change, so
with metadata_csum enabled, we have to re-calc the csum.

As the first block of the dir can be either a htree root
or a normal directory block and we have different csum
calculation for these 2 types, we have to choose the right
one in ext4_rename.

btw, it is found by xfstests 013.

Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Acked-by: Darrick J. Wong <djwong@us.ibm.com>