libeigen: patch to install the find cmake script

This commit is needed for the pcl-ros 1.3.0 recipe in the
meta-ros layer, which detects the Eigen library with the provided
cmake script.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@oss.bmw-carit.de>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>