powerpc: Remove all usages of NO_IRQ

NO_IRQ has been == 0 on powerpc for just over ten years (since commit
0ebfff1491ef ("[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>
diff --git a/drivers/macintosh/smu.c b/drivers/macintosh/smu.c
index d6f72c8..08edb2c 100644
--- a/drivers/macintosh/smu.c
+++ b/drivers/macintosh/smu.c
@@ -279,7 +279,7 @@
 	spin_unlock_irqrestore(&smu->lock, flags);
 
 	/* Workaround for early calls when irq isn't available */
-	if (!smu_irq_inited || smu->db_irq == NO_IRQ)
+	if (!smu_irq_inited || !smu->db_irq)
 		smu_spinwait_cmd(cmd);
 
 	return 0;
@@ -498,8 +498,8 @@
 	INIT_LIST_HEAD(&smu->cmd_list);
 	INIT_LIST_HEAD(&smu->cmd_i2c_list);
 	smu->of_node = np;
-	smu->db_irq = NO_IRQ;
-	smu->msg_irq = NO_IRQ;
+	smu->db_irq = 0;
+	smu->msg_irq = 0;
 
 	/* smu_cmdbuf_abs is in the low 2G of RAM, can be converted to a
 	 * 32 bits value safely
@@ -587,13 +587,13 @@
 
 	if (smu->db_node) {
 		smu->db_irq = irq_of_parse_and_map(smu->db_node, 0);
-		if (smu->db_irq == NO_IRQ)
+		if (!smu->db_irq)
 			printk(KERN_ERR "smu: failed to map irq for node %s\n",
 			       smu->db_node->full_name);
 	}
 	if (smu->msg_node) {
 		smu->msg_irq = irq_of_parse_and_map(smu->msg_node, 0);
-		if (smu->msg_irq == NO_IRQ)
+		if (!smu->msg_irq)
 			printk(KERN_ERR "smu: failed to map irq for node %s\n",
 			       smu->msg_node->full_name);
 	}
@@ -602,23 +602,23 @@
 	 * Try to request the interrupts
 	 */
 
-	if (smu->db_irq != NO_IRQ) {
+	if (smu->db_irq) {
 		if (request_irq(smu->db_irq, smu_db_intr,
 				IRQF_SHARED, "SMU doorbell", smu) < 0) {
 			printk(KERN_WARNING "SMU: can't "
 			       "request interrupt %d\n",
 			       smu->db_irq);
-			smu->db_irq = NO_IRQ;
+			smu->db_irq = 0;
 		}
 	}
 
-	if (smu->msg_irq != NO_IRQ) {
+	if (smu->msg_irq) {
 		if (request_irq(smu->msg_irq, smu_msg_intr,
 				IRQF_SHARED, "SMU message", smu) < 0) {
 			printk(KERN_WARNING "SMU: can't "
 			       "request interrupt %d\n",
 			       smu->msg_irq);
-			smu->msg_irq = NO_IRQ;
+			smu->msg_irq = 0;
 		}
 	}