target/s390x: Fix VSTL with a large length

The length is always truncated to 16 bytes. Do not probe more than
that.

Cc: qemu-stable@nongnu.org
Fixes: 0e0a5b4 ("s390x/tcg: Implement VECTOR STORE WITH LENGTH")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230804235624.263260-1-iii@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 6db3518)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target/s390x/tcg/vec_helper.c

@@ -193,7 +193,7 @@ void HELPER(vstl)(CPUS390XState *env, const void *v1, uint64_t addr,
                   uint64_t bytes)
 {
     /* Probe write access before actually modifying memory */
-    probe_write_access(env, addr, bytes, GETPC());
+    probe_write_access(env, addr, MIN(bytes, 16), GETPC());
 
     if (likely(bytes >= 16)) {
         cpu_stq_data_ra(env, addr, s390_vec_read_element64(v1, 0), GETPC());