Add typo about log-structured fs chapter order

[RheingoldRiver]

Hi, this is a small typo / I think the chapter order was changed but the wording here wasn't updated to reflect it.

As other PRs to this repo have said, thank you so much for this textbook! I've enjoyed reading it so much, it's so engaging!

[remzi-arpacidusseau]

Thanks! (for the fix and kind words). Fixes and ack in the preface to you to be uploaded soon!