PCI / PM: handle failure to enable wakeup on PCIe PME

If the irqchip handling the PCIe PME interrupt is not able
to enable interrupt wakeup we should properly reflect this
in the PME suspend status.

This fixes a kernel warning on resume, where it would try
to disable the irq wakeup that failed to be activated while
suspending, for example:

WARNING: CPU: 0 PID: 609 at kernel/irq/manage.c:536 irq_set_irq_wake+0xc0/0xf8()
Unbalanced IRQ 384 wake disable

Fixes: 76cde7e49590 (PCI / PM: Make PCIe PME interrupts wake up from suspend-to-idle)
Reported-and-tested-by: Richard Zhu <richard.zhu@freescale.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Merge branch 'pm-genirq'

* pm-genirq:
  PCI / PM: handle failure to enable wakeup on PCIe PME