vhost-vdpa: refine ioctl pre-processing

Switch to use 'switch' to make the codes more easier to be extended.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200804162048.22587-2-eli@mellanox.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vdpa.c

@@ -360,15 +360,16 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 	idx = array_index_nospec(idx, v->nvqs);
 	vq = &v->vqs[idx];
 
-	if (cmd == VHOST_VDPA_SET_VRING_ENABLE) {
+	switch (cmd) {
+	case VHOST_VDPA_SET_VRING_ENABLE:
 		if (copy_from_user(&s, argp, sizeof(s)))
 			return -EFAULT;
 		ops->set_vq_ready(vdpa, idx, s.num);
 		return 0;
-	}
-
-	if (cmd == VHOST_GET_VRING_BASE)
+	case VHOST_GET_VRING_BASE:
 		vq->last_avail_idx = ops->get_vq_state(v->vdpa, idx);
+		break;
+	}
 
 	r = vhost_vring_ioctl(&v->vdev, cmd, argp);
 	if (r)