ACPI: dock: fix enum-conversion warning

gcc points out a type mismatch:

drivers/acpi/dock.c: In function 'hot_remove_dock_devices':
drivers/acpi/dock.c:234:53: warning: implicit conversion from 'enum <anonymous>' to 'enum dock_callback_type' [-Wenum-conversion]
  234 |   dock_hotplug_event(dd, ACPI_NOTIFY_EJECT_REQUEST, false);

This is harmless because 'false' still has the correct numeric value,
but passing DOCK_CALL_HANDLER documents better what is going on
and avoids the warning.

Fixes: 37f90877 ("ACPI / dock: Walk list in reverse order during removal of devices")
Fixes: f09ce741 ("ACPI / dock / PCI: Drop ACPI dock notifier chain")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>