it87: Cleanup set_fan_div

it87: Cleanup set_fan_div

We only change one fan clock divider at a time, so there is only one
fan min which needs to be saved and restored.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>