package/ocrad: fix license

ocrad is licensed under GPL-2.0+ since version 0.24, here is an extract
of https://lists.gnu.org/archive/html/bug-ocrad/2014-10/msg00000.html

:

"The license has been changed to GPL version 2 or later for better GPL
compatibility. GPLv2 and GPLv2+ programs may use the library now."

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>