vdpa_sim_blk: Fix the potential leak of mgmt_dev

If the shared_buffer allocation fails, need to unregister mgmt_dev first.

Cc: stable@vger.kernel.org
Fixes: abebb162 ("vdpa_sim_blk: support shared backend")
Signed-off-by: Shawn.Shao <shawn.shao@jaguarmicro.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230821060333.1155-1-shawn.shao@jaguarmicro.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/vdpa_sim/vdpa_sim_blk.c

@@ -499,12 +499,13 @@ static int __init vdpasim_blk_init(void)
 					 GFP_KERNEL);
 		if (!shared_buffer) {
 			ret = -ENOMEM;
-			goto parent_err;
+			goto mgmt_dev_err;
 		}
 	}
 
 	return 0;
-
+mgmt_dev_err:
+	vdpa_mgmtdev_unregister(&mgmt_dev);
 parent_err:
 	device_unregister(&vdpasim_blk_mgmtdev);
 	return ret;