cpumask: remove last assignment to mask field of struct irqaction.

This snuck in after the patch which removed all the others.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/time.c

@@ -93,7 +93,6 @@ static struct irqaction irq0  = {
 
 void __init setup_default_timer_irq(void)
 {
-	irq0.mask = cpumask_of_cpu(0);
 	setup_irq(0, &irq0);
 }