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/drivers/extcon/extcon-rt8973a.c b/drivers/extcon/extcon-rt8973a.c
index 3e882aa..eaa355e 100644
--- a/drivers/extcon/extcon-rt8973a.c
+++ b/drivers/extcon/extcon-rt8973a.c
@@ -537,7 +537,7 @@
 		regmap_update_bits(info->regmap, reg, mask, val);
 	}
 
-	/* Check whether RT8973A is auto swithcing mode or not */
+	/* Check whether RT8973A is auto switching mode or not */
 	ret = regmap_read(info->regmap, RT8973A_REG_CONTROL1, &data);
 	if (ret) {
 		dev_err(info->dev,