drm/virtio: Fix warning in virtio_gpu_queue_fenced_ctrl_buffer.

Fix warning introduced with commit e1218b8c
("drm/virtio: Use vmalloc for command buffer allocations.")
from drm-misc-next.
Signed-off-by: David Riley <davidriley@chromium.org>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190912160048.212495-1-davidriley@chromium.orgSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_vq.c

@@ -358,7 +358,7 @@ static void virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
 			sgt = vmalloc_to_sgt(vbuf->data_buf, vbuf->data_size,
 					     &outcnt);
 			if (!sgt)
-				return -ENOMEM;
+				return;
 			vout = sgt->sgl;
 		} else {
 			sg_init_one(&sg, vbuf->data_buf, vbuf->data_size);