platform/x86: dell-sysman: Improve instance detection

The WMI driver core already knows how many WMI object instances
are available, use this information instead of probing the WMI object
manually.

Compile-tested only.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20230430203153.5587-3-W_Armin@gmx.de


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>