s390x assembly pack: fix restoring of SIGILL action

Signed-off-by: Patrick Steuer <patrick.steuer@de.ibm.com>

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9381)

(cherry picked from commit c17d60ea293746d7cd06a910ced446edbb6c1eba)