DocBook: fix various typos

This patch fixed spelling typo in various template files
within Documentation/Docbook.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl
index 19f2a5a..e584ee1 100644
--- a/Documentation/DocBook/kernel-locking.tmpl
+++ b/Documentation/DocBook/kernel-locking.tmpl
@@ -1760,7 +1760,7 @@
 </para>
 
 <para>
-There is a furthur optimization possible here: remember our original
+There is a further optimization possible here: remember our original
 cache code, where there were no reference counts and the caller simply
 held the lock whenever using the object?  This is still possible: if
 you hold the lock, no one can delete the object, so you don't need to