PM / wakeirq: fix wakeirq setting after wakup re-configuration from sysfs

Now wakeirq stops working for device if wakeup option for
this device will be reconfigured through sysfs, like:

echo disabled > /sys/devices/platform/extcon_usb1/power/wakeup
echo enabled > /sys/devices/platform/extcon_usb1/power/wakeup

Once above set of commands is executed the device's wakeup_source
opject will be recreated and dev->power.wakeup->wakeirq field will
contain NULL. As result, device_wakeup_arm_wake_irqs() will not arm
wakeirq for the affected device.

Hece, lets try to fix it in the following way:
  check for dev->wakeirq field when device_wakeup_attach() is called
  and if !NULL re-attach wakeirq to the device
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/wakeup.c

@@ -246,6 +246,8 @@ static int device_wakeup_attach(struct device *dev, struct wakeup_source *ws)
 		return -EEXIST;
 	}
 	dev->power.wakeup = ws;
+	if (dev->power.wakeirq)
+		device_wakeup_attach_irq(dev, dev->power.wakeirq);
 	spin_unlock_irq(&dev->power.lock);
 	return 0;
 }