platform/x86: ideapad-laptop: Set max_brightness before using it

platform/x86: ideapad-laptop: Set max_brightness before using it

max_brightness is used in ideapad_kbd_bl_brightness_get() before it's set,
causing ideapad_kbd_bl_brightness_get() to return -EINVAL sometimes.

Fixes: ecaa1867b524 ("platform/x86: ideapad-laptop: Add support for keyboard backlights using KBLC ACPI symbol")
Signed-off-by: Stuart Hayhurst <stuart.a.hayhurst@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20231114114055.6220-2-stuart.a.hayhurst@gmail.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>