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/kernel/i8259.c

@@ -306,7 +306,6 @@ static void init_8259A(int auto_eoi)
  */
 static struct irqaction irq2 = {
 	.handler = no_action,
-	.mask = CPU_MASK_NONE,
 	.name = "cascade",
 };