[POWERPC] Fix xics set_affinity code

On a POWER6 machine running 2.6.23-rc8 I sometimes see the following error:

xics_set_affinity: No online cpus in the mask 00000000,00000000,00000000,00000001 for irq 20

In a desperate attempt to get a changelog entry in 2.6.23, I took a look
into it.

It turns out we are passing a real and not a virtual irq into
get_irq_server.  This works for the case where hwirq < NR_IRQS and we
set virq = hwirq.  In my case however hwirq = 590082 and we try and
access irq_desc[590082], slightly past the end at 512 entries.

Lucky we ship lots of memory with our machines.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/platforms/pseries/xics.c

@@ -419,7 +419,7 @@ static void xics_set_affinity(unsigned int virq, cpumask_t cpumask)
 	 * For the moment only implement delivery to all cpus or one cpu.
 	 * Get current irq_server for the given irq
 	 */
-	irq_server = get_irq_server(irq, 1);
+	irq_server = get_irq_server(virq, 1);
 	if (irq_server == -1) {
 		char cpulist[128];
 		cpumask_scnprintf(cpulist, sizeof(cpulist), cpumask);