kernel-doc: alphabetically-sorted entries in index.html of 'htmldocs'

Make docbook index.html contain sorted output.

I prefer to let the computer do it.  This also avoids
people not reading the comment(s).
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Documentation/DocBook/Makefile

@@ -41,7 +41,7 @@ psdocs: $(PS)
 PDF := $(patsubst %.xml, %.pdf, $(BOOKS))
 pdfdocs: $(PDF)
 
-HTML := $(patsubst %.xml, %.html, $(BOOKS))
+HTML := $(sort $(patsubst %.xml, %.html, $(BOOKS)))
 htmldocs: $(HTML)
 
 MAN := $(patsubst %.xml, %.9, $(BOOKS))