Thermal: int3406_thermal: fix thermal sysfs I/F

there are three concepts represent backlight in int3406_thermal driver.
1. the raw brightness value from native graphics driver.
2. the percentage numbers from ACPI _BCL control method.
3. the consecutive numbers represent cooling states.

int3406_thermal driver
1. uses value from DDDL/DDPC as the lower/upper limit, which is consistent
   with ACPI _BCL control methods.
2. reads current and maximum brightness from the native graphics driver.
3. expose them to thermal sysfs I/F

This patch fixes the code that switches between the raw brightness value
and the cooling state, which results in bogus value in thermal sysfs I/F.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>