target/s390x: Use void* for haddr in S390Access

The interface from probe_access_flags is void*, and matching
that will be helpful.  We already rely on the gcc extension
for byte arithmetic on void*.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-Id: <20230109201856.3916639-4-richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>