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/cell/spider-pic.c

@@ -207,11 +207,11 @@ static void spider_irq_cascade(struct irq_desc *desc)
 
 	cs = in_be32(pic->regs + TIR_CS) >> 24;
 	if (cs == SPIDER_IRQ_INVALID)
-		virq = NO_IRQ;
+		virq = 0;
 	else
 		virq = irq_linear_revmap(pic->host, cs);
 
-	if (virq != NO_IRQ)
+	if (virq)
 		generic_handle_irq(virq);
 
 	chip->irq_eoi(&desc->irq_data);
@@ -245,19 +245,19 @@ static unsigned int __init spider_find_cascade_and_node(struct spider_pic *pic)
 	/* Now do the horrible hacks */
 	tmp = of_get_property(of_node, "#interrupt-cells", NULL);
 	if (tmp == NULL)
-		return NO_IRQ;
+		return 0;
 	intsize = *tmp;
 	imap = of_get_property(of_node, "interrupt-map", &imaplen);
 	if (imap == NULL || imaplen < (intsize + 1))
-		return NO_IRQ;
+		return 0;
 	iic = of_find_node_by_phandle(imap[intsize]);
 	if (iic == NULL)
-		return NO_IRQ;
+		return 0;
 	imap += intsize + 1;
 	tmp = of_get_property(iic, "#interrupt-cells", NULL);
 	if (tmp == NULL) {
 		of_node_put(iic);
-		return NO_IRQ;
+		return 0;
 	}
 	intsize = *tmp;
 	/* Assume unit is last entry of interrupt specifier */
@@ -266,7 +266,7 @@ static unsigned int __init spider_find_cascade_and_node(struct spider_pic *pic)
 	tmp = of_get_property(iic, "ibm,interrupt-server-ranges", NULL);
 	if (tmp == NULL) {
 		of_node_put(iic);
-		return NO_IRQ;
+		return 0;
 	}
 	/* ugly as hell but works for now */
 	pic->node_id = (*tmp) >> 1;
@@ -281,7 +281,7 @@ static unsigned int __init spider_find_cascade_and_node(struct spider_pic *pic)
 				  (pic->node_id << IIC_IRQ_NODE_SHIFT) |
 				  (2 << IIC_IRQ_CLASS_SHIFT) |
 				  unit);
-	if (virq == NO_IRQ)
+	if (!virq)
 		printk(KERN_ERR "spider_pic: failed to map cascade !");
 	return virq;
 }
@@ -318,7 +318,7 @@ static void __init spider_init_one(struct device_node *of_node, int chip,
 
 	/* Hook up the cascade interrupt to the iic and nodeid */
 	virq = spider_find_cascade_and_node(pic);
-	if (virq == NO_IRQ)
+	if (!virq)
 		return;
 	irq_set_handler_data(virq, pic);
 	irq_set_chained_handler(virq, spider_irq_cascade);