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/embedded6xx/hlwd-pic.c

@@ -114,7 +114,7 @@ static unsigned int __hlwd_pic_get_irq(struct irq_domain *h)
 	irq_status = in_be32(io_base + HW_BROADWAY_ICR) &
 		     in_be32(io_base + HW_BROADWAY_IMR);
 	if (irq_status == 0)
-		return NO_IRQ;	/* no more IRQs pending */
+		return 0;	/* no more IRQs pending */
 
 	irq = __ffs(irq_status);
 	return irq_linear_revmap(h, irq);
@@ -131,7 +131,7 @@ static void hlwd_pic_irq_cascade(struct irq_desc *desc)
 	raw_spin_unlock(&desc->lock);
 
 	virq = __hlwd_pic_get_irq(irq_domain);
-	if (virq != NO_IRQ)
+	if (virq)
 		generic_handle_irq(virq);
 	else
 		pr_err("spurious interrupt!\n");