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/fs/userfaultfd.c b/fs/userfaultfd.c
index 625b728..e6e0a61 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1807,17 +1807,17 @@ static void init_once_userfaultfd_ctx(void *mem)
 }
 
 /**
- * userfaultfd_file_create - Creates an userfaultfd file pointer.
+ * userfaultfd_file_create - Creates a userfaultfd file pointer.
  * @flags: Flags for the userfaultfd file.
  *
- * This function creates an userfaultfd file pointer, w/out installing
+ * This function creates a userfaultfd file pointer, w/out installing
  * it into the fd table. This is useful when the userfaultfd file is
  * used during the initialization of data structures that require
  * extra setup after the userfaultfd creation. So the userfaultfd
  * creation is split into the file pointer creation phase, and the
  * file descriptor installation phase.  In this way races with
  * userspace closing the newly installed file descriptor can be
- * avoided.  Returns an userfaultfd file pointer, or a proper error
+ * avoided.  Returns a userfaultfd file pointer, or a proper error
  * pointer.
  */
 static struct file *userfaultfd_file_create(int flags)