doc: fix generation of device-drivers

Since commit 7a6354e2

 ("sched: Move wait.c into kernel/sched/"), the
path of this file has changed.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Andy Whitcroft <apw@canonical.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>