Allocate v_object for the new snapshot vnode.

The vnode is not opened, so it ends up with the malloced buffers otherwise.

Reported and tested by:	pho
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation

sys/ufs/ffs/ffs_snapshot.c

@@ -302,6 +302,7 @@ restart:
 		return (error);
 	}
 	vp = nd.ni_vp;
+	vnode_create_vobject(nd.ni_vp, fs->fs_size, td);
 	vp->v_vflag |= VV_SYSTEM;
 	ip = VTOI(vp);
 	devvp = ITODEVVP(ip);