drivers: power_domain: gpio_monitor: Fix compilation error

The fix 25173f71cd created
`struct pm_device_base` and moved `usage` to it.
This has been overlooked so that I fixed it.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

drivers/power_domain/power_domain_gpio_monitor.c

@@ -39,7 +39,7 @@ static int pd_on_domain_visitor(const struct device *dev, void *context)
 		return 0;
 	}
 
-	dev->pm->usage = 0;
+	dev->pm->base.usage = 0;
 	(void)pm_device_action_run(dev, visitor_context->action);
 	return 0;
 }