target/s390x: Use a 16-bit immediate in VREP

target/s390x: Use a 16-bit immediate in VREP

Unlike most other instructions that contain an immediate element index,
VREP's one is 16-bit, and not 4-bit. The code uses only 8 bits, so
using, e.g., 0x101 does not lead to a specification exception.

Fix by checking all 16 bits.

Cc: qemu-stable@nongnu.org
Fixes: 28d08731b1d8 ("s390x/tcg: Implement VECTOR REPLICATE")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230807163459.849766-1-iii@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 23e87d419f347b6b5f4da3bf70d222acc24cdb64)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>