ACPI: scan: Fix device check notification handling

It is generally invalid to fail a Device Check notification if the scan
handler has not been attached to the given device after a bus rescan,
because there may be valid reasons for the scan handler to refuse
attaching to the device (for example, the device is not ready).

For this reason, modify acpi_scan_device_check() to return 0 in that
case without printing a warning.

While at it, reduce the log level of the "already enumerated" message
in the same function, because it is only interesting when debugging
notification handling

Fixes: 443fc820 ("ACPI / hotplug: Rework generic code to handle suprise removals")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>