The interface for backlight_device_register() changed for release 2.6.34 of the kernel.
The problem and a possible solution are described in more detail at
Please consider the patch attached (or a similar one) for inclusion
The suggested patch introduces a compiler warning, I made that choice to avoid more preprocessor commands as I feel that they seriously hinder readability. If your policy is against compiler warnings, I can easily rewrite it in such a way that no warnings are issued!