backlight: Just match amdgpu_bl prefix (#2122)
backlight: Just match amdgpu_bl prefix (#2122)

Some devices can have "amdgpu_bl1" or "amdgpu_bl2", but the code hardcoded in the value "amdgpu_bl0". This change tests based on the first characters: "amdgpu_bl".
jaagr/polybar,jaagr/polybar,jaagr/polybar