vhost/scsi: fix up req type endian-ness

vhost/scsi doesn't handle type conversion correctly
for request type when using virtio 1.0 and up for BE,
or cross-endian platforms.

Fix it up using vhost_32_to_cpu.

Cc: stable@vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>