nilfs2: fix various typos in comments

This fixes various typos I found in comments of nilfs2.

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

fs/nilfs2/dat.c

@@ -288,7 +288,7 @@ int nilfs_dat_mark_dirty(struct inode *dat, __u64 vblocknr)
  * @vblocknrs and @nitems.
  *
  * Return Value: On success, 0 is returned. On error, one of the following
- * nagative error codes is returned.
+ * negative error codes is returned.
  *
  * %-EIO - I/O error.
  *