Brightness control not working (Toshiba Satellite C670D - AMD Radeon HD 6310)

Hey all,

Since today my FN buttons to adjust the screen brightness stopped working.
The volume buttons still work fine. I have installed Kali Linux on my HDD.
My laptop is a Toshiba Satellite C670D with AMD Radeon HD 6310 and I am using GNOME.
As far as I can remember I have not (un)installed anything lately.

I hope I provided enough information, I'm kind of new to this.

Sorry if I forgot anything, and thanks in advance.