ACPI: PM: s2idle: Avoid rearming SCI for wakeup unnecessarily

It is only necessary to rearm the ACPI SCI for wakeup if
pm_system_cancel_wakeup() has been called, so invoke
rearm_wake_irq() only in that case.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>