linux: fix COPYING file hash

In version 5.6 a minor change was made to this file, stating tht "[a]ll
contributions to the Linux Kernel are subject to this COPYING file",
and hence the hash changed.

We can update the hash, because the licensing information is only
accounted for the "latest" version, so the hash change will not impact
older kernel versions as the user would have to switch to a non-latest
kernel.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>