platform/x86: compal-laptop: Use backlight helper

platform/x86: compal-laptop: Use backlight helper

Instead of manually checking the power state in struct
backlight_properties, use backlight_is_blank().

Signed-off-by: Stephen Kitt <steve@sk2.org>
Cc: Cezary Jackiewicz <cezary.jackiewicz@gmail.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mark Gross <markgross@kernel.org>
Cc: platform-driver-x86@vger.kernel.org
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20220607184635.1127913-4-steve@sk2.org
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>