Keyboard backlight timeout control script doesn't work when dell-smbios-wmi in use

This problem is related to (and a possible regression of) #48.

My problem is that I cannot set the keyboard timeout with `smbios-keyboard-ctl`. The output I get when trying to do so is:

```
Setting keyboard illumination timeout value of: 1h
ERROR: Could not execute SMI.

Common problems are:

-- 'SMM Mitigations' is enabled in BIOS setup.
Run kernel 4.15 or later with
dell-smbios-wmi enabled.
or
Disable 'SMM mitigations' in BIOS setup.

-- Insufficient permissions to perform operation.
Try running as a more privileged account.
Linux : run as 'root' user
Windows: run as 'administrator' user

-- dell-smbios-wmi driver not loaded
Try loading the dell-smbios-wmi driver
Linux : modprobe dell-smbios-wmi

-- Call filtered by Linux kernel
Some functionality is natively supported
by the Linux kernel

-- dcdbas device driver not loaded.
Try loading the dcdbas driver
Linux : modprobe dcdbas
```

In #48 I gathered that this was related to a bug in the BIOS so I proceeded to update my BIOS. I was running 1.3.1 before, the fix was introduced in 1.4.0. I'm currently running 1.5.0 but the problem is still there. I don't know if this is still something that should be fixed upstream, if so, please point me in the right direction as to where I can report this.

I should add, as well, that I was running under X11 before, but with the BIOS update I could no longer log into my window manager. Only as far as the Gnome's login handler. Switching to Wayland fixed this. So I'm now running a different WM/Display driver! If you could help point me in the direction where to report this issue, that would be great as well.

I'm using the new XPS 9570 w/o touch.