If we have a threaded interrupt with the handler being NULL, then
request_threaded_irq() -> __setup_irq() will complain and bail out if the
IRQF_ONESHOT flag isn't set.  Therefore check for the handler being NULL
and set IRQF_ONESHOT in this case.

This change is needed to migrate the mei_me driver to
pci_alloc_irq_vectors() and pci_request_irq().
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>