Fix chapter reference in CodingStyle

commit 226a6b84 renumbered Chapter 11 in
Documentation/CodingStyle to Chapter 12, but it didn't update the reference
to that chapter further down in the file.  This patch corrects the chapter
reference.

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>