Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/mm/internal.h b/mm/internal.h
index 3438dd4..9d0ced8 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -162,7 +162,7 @@
 }
 
 /*
- * Iterator over all subpages withing the maximally aligned gigantic
+ * Iterator over all subpages within the maximally aligned gigantic
  * page 'base'.  Handle any discontiguity in the mem_map.
  */
 static inline struct page *mem_map_next(struct page *iter,