At present the counter never hits the comparitor in this case. Add a
special case.
This ensures that the snow backlight works when at full brightness.
Fixes: 76c2ff3e5fd video: backlight: fix pwm's duty cycle calculation
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>