locking, hpet: annotate false positive warning

Alexander Beregalov reported that this warning is caused by the HPET code:

> hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0
> hpet0: 3 comparators, 64-bit 14.318180 MHz counter
> ODEBUG: object is on stack, but not annotated
> ------------[ cut here ]------------
> WARNING: at lib/debugobjects.c:251 __debug_object_init+0x2a4/0x352()

> Bisected down to 26afe5f2
> (x86: HPET_MSI Initialise per-cpu HPET timers)

The commit is fine - but the on-stack workqueue entry needs annotation.

Reported-and-bisected-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>