eeepc-laptop: replace magic numbers with defines

eeepc_[gs]et_fan_ctrl uses some magic numbers. These numbers mean
something more than just the number. Describe them with macros instead
of comments in one of the functions.

Signed-off-by: Frans Klaver <fransklaver@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>