ACPI / PCI: acpi_pci_irq_enable() must return an error if ACPI cannot map an IRQ.

ACPI / PCI: acpi_pci_irq_enable() must return an error if ACPI cannot map an IRQ.

Driver probe's currently do the following

	pci_enable_device();
	/* ... do some other init stuff, and eventually call ... */
	request_irq();

After pci_enable_device() is called it is assumed that the device's
irq value (pci_dev->irq) has been appropriately set on success.  This
value is passed into the request_irq() call.

In the case that ACPI is used to determine the irq value, it is
possible that the ACPI IRQ look up for a specific device fails and
success is returned by pci_enable_device().

The call sequence is:

pci_enable_device();
	-> pci_enable_device_flags();
		->do_pci_enable_device();
			-> pcibios_enable_device() which, if the device
			   does not use MSI calls
			   -> pcibios_enable_irq() which maps to
			      acpi_pci_irq_enable()
				-> acpi_pci_irq_lookup()

If acpi_pci_irq_lookup() cannot map the device's IRQ value it returns
NULL as an error.  The error is returned to acpi_pci_irq_enable(),
but is not propagated further.  This can result in the driver
returning success for pci_enable_device() and the driver probe
attempting to call request_irq() with dev->irq = 0.

This patch modifies acpi_pci_irq_enable() to return an error in the
case that an entry is not found in the ACPI tables.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>