target/s390x: Fix MXDB and MXDBR

target/s390x: Fix MXDB and MXDBR

These instructions multiply 64 bits by 64 bits, not 128 bits by 64 bits.

Reported-by: Tulio Magno Quites Machado Filho <tuliom@redhat.com>
Fixes: 2b91240f95fd ("target/s390x: Use Int128 for passing float128")
Cc: qemu-stable@nongnu.org
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2211472
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230601223027.795501-2-iii@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>