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

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

  swith||switch
  swithable||switchable
  swithed||switched
  swithing||switching

While we are here, fix the "update" to "updates" in the touched hunk in
drivers/net/wireless/marvell/mwifiex/wmm.c.

Link: http://lkml.kernel.org/r/1481573103-11329-2-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/arm/mm/cache-v7m.S

@@ -217,7 +217,7 @@ skip:
 	cmp	r3, r10
 	bgt	flush_levels
 finished:
-	mov	r10, #0				@ swith back to cache level 0
+	mov	r10, #0				@ switch back to cache level 0
 	write_csselr r10, r3			@ select current cache level in cssr
 	dsb	st
 	isb