drivers/char: for hpet, add count checking, and ~0UL instead of -1

drivers/char: for hpet, add count checking, and ~0UL instead of -1

  use ~0UL for unsigned long variable initialization, instead of -1.

  add check for hdp->hd_nirqs within 32 (HPET_MAX_TIMERS).
    the type of irqp->interrupt_count is u8.
    the git diff not display the relative lines below.
      hdp->hd_irq[hdp->hd_nirqs] = irq;
      hdp->hd_nirqs++;
    please check source code to get more information.

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>