irq: use WARN() instead of WARN_ON().

Impact: cleanup WARN msg.

Ingo requested:
> While at it, could you please also convert this to a WARN() construct
> instead? (in a separate commit)

... and it shall be done.  ;-)
Signed-off-by: Mike Travis <travis@sgi.com>

kernel/irq/handle.c

@@ -163,9 +163,8 @@ struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu)
 	int node;
 
 	if (irq >= nr_irqs) {
-		printk(KERN_WARNING "irq >= nr_irqs in irq_to_desc_alloc: %d %d\n",
-				irq, nr_irqs);
-		WARN_ON(1);
+		WARN(1, "irq (%d) >= nr_irqs (%d) in irq_to_desc_alloc\n",
+			irq, nr_irqs);
 		return NULL;
 	}