nilfs2: use iget for all metadata files

This makes use of iget5_locked to allocate or get inode for metadata
files to stop using own inode allocator.

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/ifile.c
Simple merge

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

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

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

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

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

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

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

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

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