docbook: fix sched source file names in device-drivers book

Fix warning since kernel scheduler functions and kernel-doc
notation were moved to other files.

docproc: lnx-33-rc1/kernel/sched.c: No such file or directory
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/DocBook/device-drivers.tmpl

@@ -50,7 +50,9 @@
 
      <sect1><title>Delaying, scheduling, and timer routines</title>
 !Iinclude/linux/sched.h
-!Ekernel/sched.c
+!Ekernel/sched/core.c
+!Ikernel/sched/cpupri.c
+!Ikernel/sched/fair.c
 !Iinclude/linux/completion.h
 !Ekernel/timer.c
      </sect1>