target/s390x: Fix EXECUTE of relative branches

target/s390x: Fix EXECUTE of relative branches

Fix a problem similar to the one fixed by commit 703d03a4aaf3
("target/s390x: Fix EXECUTE of relative long instructions"), but now
for relative branches.

Reported-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230426235813.198183-2-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit e8ecdfeb30f087574191cde523e846e023911c8d)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>