vhost-vdpa: vhost_vdpa_alloc_domain() should be using a const struct bus_type *

vhost-vdpa: vhost_vdpa_alloc_domain() should be using a const struct bus_type *

The function, vhost_vdpa_alloc_domain(), has a pointer to a struct
bus_type, but it should be constant as the function it passes it to
expects it to be const, and the vhost code does not modify it in any
way.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: kvm@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/r/20230313182918.1312597-31-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>