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

In "struct npcm7xx_cooling_device", the 'fan_clk_freq' field is unused.
Remove it.

Found with cppcheck, unusedStructMember.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/74eee8aa739f94b8c6425ce3e37a427ca92243ea.1714505655.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: tititiou36

drivers/hwmon/npcm750-pwm-fan.c

@@ -197,7 +197,6 @@ struct npcm7xx_pwm_fan_data {
 	void __iomem *fan_base;
 	int pwm_modules;
 	unsigned long pwm_clk_freq;
-	unsigned long fan_clk_freq;
 	struct clk *pwm_clk;
 	struct clk *fan_clk;
 	struct mutex pwm_lock[NPCM7XX_PWM_MAX_MODULES];