* We are handing back HANDLED even though the IRQ is not for us.
  We also change device state.
  This is plainly wrong.
  AFAICT we also need to take the spin lock early.
  Tested/running on UP/SMP for about a week now.
  (Discovered on one of my lappies that had the X driver on the same IRQ)
  (Proposed on Prism54 Devel with no objections)