rosserial_embeddedlinux: Fix CMakeLists.txt ...

so 'catkin_make install' can find 'examples' directory under 'src' directory in rosserial_embeddedlinux

This is so that the following part of the Arduino IDE Setup of rosserial can run properly:
http://ros.org/wiki/rosserial_arduino/Tutorials/Arduino%20IDE%20Setup#Installing_from_Source_onto_the_ROS_workstation