hwmon: (npcm750-pwm-fan) Remove another unused field in struct npcm7xx_cooling_device

In "struct npcm7xx_cooling_device", the 'pwm_clk_freq' field is only
written and never used.

Remove it and update npcm7xx_pwm_init() accordingly.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/2ff738663d40ac5ae3d0b4d2e688ff7e36032be8.1714505655.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Guenter Roeck <linux@roeck-us.net>