Fixes gcc '-Wunused-but-set-variable' warning:

drivers/hwmon/w83627ehf.c: In function 'w83627ehf_check_fan_inputs':
drivers/hwmon/w83627ehf.c:1296:24: warning:
 variable 'fan4min' set but not used [-Wunused-but-set-variable]

commit 62000264cfa8 ("hwmon: (w83627ehf) remove nct6775 and nct6776 support")
left behind this unused variable.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20200108034514.50130-1-yuehaibing@huawei.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>