hwmon: (gpio-fan) Allow to stop FANs when CONFIG_PM is disabled

hwmon: (gpio-fan) Allow to stop FANs when CONFIG_PM is disabled

When CONFIG_PM is disabled, the GPIO controlled FANs can't be stopped by
using the sysfs attributes since commit 0d01110e6356 ("hwmon: (gpio-fan)
Add regulator support").

Using either the 'pwm1' or the 'fan1_target' attribute fails the same way:

  $ echo 0 > /sys/class/hwmon/hwmon1/pwm1
  ash: write error: Function not implemented
  $ echo 0 > /sys/class/hwmon/hwmon1/fan1_target
  ash: write error: Function not implemented

Both commands were working flawlessly before the mentioned commit.

The issue happens because pm_runtime_put_sync() returns with -ENOSYS
when CONFIG_PM is disabled, and the set_fan_speed() function handles
this as an error.

In order to restore the previous behaviour, change the error check in
the set_fan_speed() function to ignore the -ENOSYS error code.

Cc: stable@vger.kernel.org
Fixes: 0d01110e6356 ("hwmon: (gpio-fan) Add regulator support")
Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
Link: https://lore.kernel.org/r/20260202-gpio-fan-stop-fix-v1-1-c7853183d93d@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>