opencv_2.4: Update LICENSE

LICENSE file at the root of the opencv repo says:

License Agreement
For Open Source Computer Vision Library
(3-clause BSD License)

Credits-to: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>