use proper native board include (#68)

You can merge this Pull Request by running:

  git pull https://github.com/LudwigOrtmann/RIOT master

Or you can view, comment on it, or merge it online at:

  https://github.com/RIOT-OS/RIOT/pull/68

-- Commit Summary --

  * use proper native board include

-- File Changes --

    M cpu/native/lpm_cpu.c (2)

-- Patch Links --

https://github.com/RIOT-OS/RIOT/pull/68.patch https://github.com/RIOT-OS/RIOT/pull/68.diff

Merged #68.