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>
diff --git a/fs/nilfs2/segbuf.c b/fs/nilfs2/segbuf.c
index 68b08f2..e3f67c6 100644
--- a/fs/nilfs2/segbuf.c
+++ b/fs/nilfs2/segbuf.c
@@ -174,7 +174,7 @@
 }
 
 /*
- * Setup segument summary
+ * Setup segment summary
  */
 void nilfs_segbuf_fill_in_segsum(struct nilfs_segment_buffer *segbuf)
 {