smu7_get_xclk() returns some crazy values when display is off. And this value
depends on some state that changes every boot.

$ sudo journalctl -b -1 -o cat | grep reference_clock | sort | uniq -c
      4 amdgpu: reference_clock = 232169472, tmp = 0
      5 amdgpu: reference_clock = 2700, tmp = 0
$ sudo journalctl -b -o cat | grep reference_clock | sort | uniq -c
     16 amdgpu: reference_clock = 1305214976, tmp = 0
     12 amdgpu: reference_clock = 2700, tmp = 0

So now after reboot I get a different FAN speed when display is off:
$ cat /sys/class/hwmon/hwmon6/fan1_input
1057

When display is on, FAN speed is always consistent.
$ cat /sys/class/hwmon/hwmon6/fan1_input
937