cpupowerutils: increase MAX_LINE_LEN

larger sysfs data (>255 bytes) was truncated and thus used improperly

[linux@dominikbrodowski.net: adapted to cpupowerutils]
Signed-off-by: Roman Vasiyarov <rvasiyarov@gmail.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>