The documentation referred to non-existent device
attributes under a non-existent platform device.
Update it with the current location of the attributes.

Fixes: b5c37b79 ("ideapad_laptop: convert ideapad device/driver to platform bus")
Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20210203215403.290792-29-pobrn@protonmail.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>