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/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 2fd7586..1cda352 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4102,7 +4102,7 @@
 				 * as a SMAP violation if all of the following
 				 * conditions are ture:
 				 *   - X86_CR4_SMAP is set in CR4
-				 *   - An user page is accessed
+				 *   - A user page is accessed
 				 *   - Page fault in kernel mode
 				 *   - if CPL = 3 or X86_EFLAGS_AC is clear
 				 *