powerpc: Remove all usages of NO_IRQ

NO_IRQ has been == 0 on powerpc for just over ten years (since commit
0ebfff1491 ("[POWERPC] Add new interrupt mapping core and change
platforms to use it")). It's also 0 on most other arches.

Although it's fairly harmless, every now and then it causes confusion
when a driver is built on powerpc and another arch which doesn't define
NO_IRQ. There's at least 6 definitions of NO_IRQ in drivers/, at least
some of which are to work around that problem.

So we'd like to remove it. This is fairly trivial in the arch code, we
just convert:

    if (irq == NO_IRQ)	to	if (!irq)
    if (irq != NO_IRQ)	to	if (irq)
    irq = NO_IRQ;	to	irq = 0;
    return NO_IRQ;	to	return 0;

And a few other odd cases as well.

At least for now we keep the #define NO_IRQ, because there is driver
code that uses NO_IRQ and the fixes to remove those will go via other
trees.

Note we also change some occurrences in PPC sound drivers, drivers/ps3,
and drivers/macintosh.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/pci-cxl.c

@@ -344,7 +344,7 @@ int pnv_cxl_cx4_setup_msi_irqs(struct pci_dev *pdev, int nvec, int type)
 			return (hwirq ? hwirq : -ENOMEM);
 
 		virq = irq_create_mapping(NULL, hwirq);
-		if (virq == NO_IRQ) {
+		if (!virq) {
 			pr_warn("%s: Failed to map cxl mode MSI to linux irq\n",
 				pci_name(pdev));
 			return -ENOMEM;
@@ -374,7 +374,7 @@ void pnv_cxl_cx4_teardown_msi_irqs(struct pci_dev *pdev)
 		return;
 
 	for_each_pci_msi_entry(entry, pdev) {
-		if (entry->irq == NO_IRQ)
+		if (!entry->irq)
 			continue;
 		hwirq = virq_to_hw(entry->irq);
 		irq_set_msi_desc(entry->irq, NULL);