Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 4c01249..e5498d7 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -313,7 +313,7 @@
  * restarted (i.e. we have flagged this in the sys_private entry of the
  * info block).
  *
- * To protect aginst the timer going away while the interrupt is queued,
+ * To protect against the timer going away while the interrupt is queued,
  * we require that the it_requeue_pending flag be set.
  */
 void do_schedule_next_timer(struct siginfo *info)