[LITMUS^RT] Two simple compile-time fixes for LITMUS^RT staging.

[Christopher Kenna]

Two simple fixes I noticed while compiling LITMUS^RT (staging). I pushed this
into a prop/compile-fixes branch on GitHub, too:

https://github.com/LITMUS-RT/litmus-rt/commits/prop/compile-fixes

The commits are:
[PATCH 1/2] Fix changed task_struct field name.
[PATCH 2/2] Include a missing header file.