ceph: fix llistxattr on symlink

only regular file and directory have vxattrs.

Signed-off-by: Yan, Zheng <[e-mail]>

fs/ceph/xattr.c

···
 		return ceph_dir_vxattrs_name_size;
 	if (vxattrs == ceph_file_vxattrs)
 		return ceph_file_vxattrs_name_size;
-	BUG();
-
+	BUG_ON(vxattrs);
 	return 0;
 }