MAINTAINERS: add vhost-scsi entry and myself as a co-maintainer

I've been doing a lot of the development on vhost-scsi the last couple of
years, so per Michael T's suggestion this adds me as co-maintainer.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20230715142027.5572-1-michael.christie@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>