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/sysdev/xics/icp-native.c

@@ -124,10 +124,10 @@ static unsigned int icp_native_get_irq(void)
 	unsigned int irq;
 
 	if (vec == XICS_IRQ_SPURIOUS)
-		return NO_IRQ;
+		return 0;
 
 	irq = irq_find_mapping(xics_host, vec);
-	if (likely(irq != NO_IRQ)) {
+	if (likely(irq)) {
 		xics_push_cppr(vec);
 		return irq;
 	}
@@ -138,7 +138,7 @@ static unsigned int icp_native_get_irq(void)
 	/* We might learn about it later, so EOI it */
 	icp_native_set_xirr(xirr);
 
-	return NO_IRQ;
+	return 0;
 }
 
 #ifdef CONFIG_SMP