f2fs: fix typo in comments

Correct spelling typo in comments

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 06ff6a5..5bb87e0 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -141,7 +141,7 @@
 	rwlock_t ext_lock;	/* rwlock for consistency */
 	unsigned int fofs;	/* start offset in a file */
 	u32 blk_addr;		/* start block address of the extent */
-	unsigned int len;	/* lenth of the extent */
+	unsigned int len;	/* length of the extent */
 };
 
 /*