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

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

  an user||a user
  an userspace||a userspace

I also added "userspace" to the list since it is a common word in Linux.
I found some instances for "an userfaultfd", but I did not add it to the
list.  I felt it is endless to find words that start with "user" such as
"userland" etc., so must draw a line somewhere.

Link: http://lkml.kernel.org/r/1481573103-11329-4-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/include/net/mac80211.h b/include/net/mac80211.h
index b9a08cd..a3bab3c 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -3392,7 +3392,7 @@ enum ieee80211_reconfig_type {
  *	since there won't be any time to beacon before the switch anyway.
  * @pre_channel_switch: This is an optional callback that is called
  *	before a channel switch procedure is started (ie. when a STA
- *	gets a CSA or an userspace initiated channel-switch), allowing
+ *	gets a CSA or a userspace initiated channel-switch), allowing
  *	the driver to prepare for the channel switch.
  * @post_channel_switch: This is an optional callback that is called
  *	after a channel switch procedure is completed, allowing the