alpha: use set_irq_chip and push down __do_IRQ to the machine types

Also kill superfluous IRQ_DISABLED initialization, since that's the
default state of the irq_desc[i].status field.

Tested-by: Michael Cree <mcree@orcon.net.nz>
Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>
diff --git a/arch/alpha/kernel/sys_titan.c b/arch/alpha/kernel/sys_titan.c
index 9008d0f..ffa48e8 100644
--- a/arch/alpha/kernel/sys_titan.c
+++ b/arch/alpha/kernel/sys_titan.c
@@ -189,8 +189,8 @@
 {
 	long i;
 	for (i = imin; i <= imax; ++i) {
-		irq_desc[i].status = IRQ_DISABLED | IRQ_LEVEL;
-		irq_desc[i].chip = ops;
+		irq_desc[i].status |= IRQ_LEVEL;
+		set_irq_chip_and_handler(i, ops, alpha_do_IRQ);
 	}
 }