cpumask: remove references to struct irqaction's mask field.

Impact: cleanup

It's unused, since about 1995.  So remove all initialization of it in
preparation for actually removing the field.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Thomas Gleixner <tglx@linutronix.de>

arch/mips/cobalt/irq.c

@@ -47,7 +47,6 @@ asmlinkage void plat_irq_dispatch(void)
 
 static struct irqaction cascade = {
 	.handler	= no_action,
-	.mask		= CPU_MASK_NONE,
 	.name		= "cascade",
 };