hwmon: (npcm750-pwm) Add an error code check in npcm7xx_en_pwm_fan

npcm7xx_pwm_config_set() can return '-ENODEV' for failed. So check
the value of 'ret' after calling npcm7xx_pwm_config_set().

Signed-off-by: Su Hui <suhui@nfschina.com>
Link: https://lore.kernel.org/r/20231020085518.198477-1-suhui@nfschina.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>