vhost: fix VHOST_*_OWNER documentation

VHOST_OWNER_SET and VHOST_OWNER_RESET are used in the documentation
instead of VHOST_SET_OWNER and VHOST_RESET_OWNER respectively.

To avoid confusion, let's use the right names in the documentation.
No change to the API, only the documentation is involved.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20250303085237.19990-1-sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>