hwmon: (adm9240) fix data race in adm9240_fan_read

In
adm9240_read()
  adm9240_fan_read()
    adm9240_write_fan_div(),

it assumes that the caller of adm9240_write_fan_div() must hold
data->update_lock. Otherwise, it may cause data races when data is
updated by other threads.

Signed-off-by: Li Zhong <floridsleeves@gmail.com>
Link: https://lore.kernel.org/r/20220924001751.1726369-1-floridsleeves@gmail.com


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