docbook: fix fatal rapidio yet again (and more to come)

Don't refer to file that no longer exists:
docproc: linux-2.6.25-git14/arch/powerpc/kernel/rio.c: No such file or directory

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>