nilfs2: fix block comments

This fixes block comments with proper formatting to eliminate the
following checkpatch.pl warnings:

  "WARNING: Block comments use * on subsequent lines"
  "WARNING: Block comments use a trailing */ on a separate line"

Link: http://lkml.kernel.org/r/1462886671-3521-8-git-send-email-konishi.ryusuke@lab.ntt.co.jp


Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>