platform/x86: thinkpad_acpi: Stop setting led_classdev brightness directly

There is no need to set the led_classdev's brightness value from
its set_brightness callback, this is taken care of by the led-core and
thinkpad_acpi really should not be mucking with it.

Note that kbdlight_set_level_and_update() is still used by the old
thinpad_acpi specific sysfs interface for the led, so we cannot
remove it.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Pavel Machek <pavel@ucw.cz>