thermal: rockchip: fixes invalid temperature case

The temp_to_code function will return 0 when we set the temperature to a
invalid value (e.g. 61C, 62C, 63C....), that's unpractical. This patch
will prevent this case happening. That will return the max analog value to
indicate the temperature is invalid or over table temperature range.

Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>