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/kernel/irq/manage.c b/kernel/irq/manage.c
index 6b66959..944d068 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -353,7 +353,7 @@ static int setup_affinity(struct irq_desc *desc, struct cpumask *mask)
 		return 0;
 
 	/*
-	 * Preserve the managed affinity setting and an userspace affinity
+	 * Preserve the managed affinity setting and a userspace affinity
 	 * setup, but make sure that one of the targets is online.
 	 */
 	if (irqd_affinity_is_managed(&desc->irq_data) ||