Since the "2 | 3+" expression can be simplified as "2+",
it is pointless to mention the GPLv3 license.

Add the corresponding SPDX identifier to remove all doubt.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>