tree-wide: fix 'lenght' typo in comments and code

Some misspelled occurences of 'octet' and some comments were also fixed
as I was on it.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Jiri Kosina <trivial@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index d34afad..b794dd8 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -69,7 +69,7 @@
  *
  * pa_lstart -> the logical start block for this prealloc space
  * pa_pstart -> the physical start block for this prealloc space
- * pa_len    -> lenght for this prealloc space
+ * pa_len    -> length for this prealloc space
  * pa_free   ->  free space available in this prealloc space
  *
  * The inode preallocation space is used looking at the _logical_ start