ARM: mach-shmobile: sh73a0 gic_arch_extn.irq_set_wake() fix

Initialize ->irq_set_wake() in gic_arch_extn to unbreak wake
up from the KEYSC device on AG5EVM in case of Suspend-to-RAM.

Without this patch "echo mem > /sys/power/state" and a key
press results in the following message on resume:

WARNING: at kernel/irq/manage.c:507 irq_set_irq_wake+0x7c/0xd8()
Unbalanced IRQ 103 wake disable

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>