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

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

  swithc||switch
  swithced||switched
  swithcing||switching

Link: http://lkml.kernel.org/r/1481573103-11329-3-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>
diff --git a/scripts/spelling.txt b/scripts/spelling.txt
index 10df6d0..372840a 100644
--- a/scripts/spelling.txt
+++ b/scripts/spelling.txt
@@ -993,6 +993,9 @@
 switchs||switches
 swith||switch
 swithable||switchable
+swithc||switch
+swithced||switched
+swithcing||switching
 swithed||switched
 swithing||switching
 symetric||symmetric