platform/x86: thinkpad_acpi: Fix max_brightness of thinklight

Thinklight has only two values, on/off so it's reasonable for
max_brightness to be 0 and 1 as if you write anything between 0 and 255
it will be 255 anyway so there's no point for it to be 255.

This may look like it is a userspace API change, but writes with
a value larget then the new max_brightness will still be accepted,
these will be silently clamped to the new max_brightness by
led_set_brightness_nosleep(). So no userspace API problems are
expected.
Reported-by: Michał Szczepaniak <m.szczepaniak.000@gmail.com>
Link: https://lore.kernel.org/platform-driver-x86/55400326-e64f-5444-94e5-22b8214d00b6@gmail.com/Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -5572,6 +5572,7 @@ static enum led_brightness light_sysfs_get(struct led_classdev *led_cdev)
 static struct tpacpi_led_classdev tpacpi_led_thinklight = {
 	.led_classdev = {
 		.name		= "tpacpi::thinklight",
+		.max_brightness	= 1,
 		.brightness_set_blocking = &light_sysfs_set,
 		.brightness_get	= &light_sysfs_get,
 	}