libseccomp: Correct LIC_FILES_CHKSUM

Previously, only the first line of the LICENSE file was included,
which only covered the license name and thus would not detect a change
to the version (or anything else for that matter).

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 3ac45755)
Signed-off-by: Steve Sakoman <steve@sakoman.com>