irq: sparse irqs, export nr_irqs

fix:

  Building modules, stage 2.
  MODPOST 458 modules
  ERROR: "nr_irqs" [drivers/serial/8250.ko] undefined!
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/irq/handle.c

@@ -48,6 +48,7 @@ handle_bad_irq(unsigned int irq, struct irq_desc *desc)
  * Controller mappings for all interrupt sources:
  */
 int nr_irqs = NR_IRQS;
+EXPORT_SYMBOL_GPL(nr_irqs);
 
 #ifdef CONFIG_HAVE_DYN_ARRAY
 static struct irq_desc irq_desc_init __initdata = {