Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index b5ed541..34591ee8 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -144,7 +144,7 @@
  *
  * Description:
  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
- *   started when this function returns, we make no guarentees on
+ *   started when this function returns, we make no guarantees on
  *   completion. Caller need not hold sb s_umount semaphore.
  *
  */