scripts/spelling.txt: add "an one" pattern and fix typo instances

Fix typos and add the following to the scripts/spelling.txt:

  an one||a one

I dropped the "an" before "one or more" in
drivers/net/ethernet/sfc/mcdi_pcol.h.

Link: http://lkml.kernel.org/r/1481573103-11329-6-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/s390/kernel/vtime.c

@@ -350,7 +350,7 @@ static void __add_vtimer(struct vtimer_list *timer, int periodic)
 }
 
 /*
- * add_virt_timer - add an oneshot virtual CPU timer
+ * add_virt_timer - add a oneshot virtual CPU timer
  */
 void add_virt_timer(struct vtimer_list *timer)
 {