Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index a12cc3f..9905501 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -377,7 +377,7 @@
  * @new: new id
  *
  * Returns old id at success, 0 at failure.
- * (There is no mem_cgroup useing 0 as its id)
+ * (There is no mem_cgroup using 0 as its id)
  */
 unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 					unsigned short old, unsigned short new)