platform/x86: ideapad-laptop: misc. device attribute changes

platform/x86: ideapad-laptop: misc. device attribute changes

Do not handle zero length buffer separately. Use kstrtouint() instead
of sscanf(). Use kstrtobool() in store_ideapad_cam(). These
introduce minor ABI changes, but it is expected that no users rely
on the previous behavior. Thus the change is deemed justifed.
Additionally, use `!!` to convert to `int` and use the "%d" format
specifier in sysfs_emit() for boolean-like attributes.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20210203215403.290792-16-pobrn@protonmail.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>