nilfs2: separate read method of meta data files on super root block

Will displace nilfs_mdt_read_inode_direct function with an individual
read method: nilfs_dat_read, nilfs_sufile_read, nilfs_cpfile_read.

This provides the opportunity to initialize local variables of each
metadata file after reading the inode.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

diff --cc fs/nilfs2/cpfile.c
Simple merge

diff --cc fs/nilfs2/cpfile.h
Simple merge

diff --cc fs/nilfs2/dat.c
Simple merge

diff --cc fs/nilfs2/dat.h
Simple merge

diff --cc fs/nilfs2/sufile.c
Simple merge

diff --cc fs/nilfs2/sufile.h
Simple merge

diff --cc fs/nilfs2/the_nilfs.c
Simple merge