simple local filesystems: switch to ->iterate_shared()

no changes needed (XFS isn't simple, but it has the same parallelism
in the interesting parts exercised from CXFS).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/xfs/xfs_file.c

@@ -1714,7 +1714,7 @@ const struct file_operations xfs_file_operations = {
 const struct file_operations xfs_dir_file_operations = {
 	.open		= xfs_dir_open,
 	.read		= generic_read_dir,
-	.iterate	= xfs_file_readdir,
+	.iterate_shared	= xfs_file_readdir,
 	.llseek		= generic_file_llseek,
 	.unlocked_ioctl	= xfs_file_ioctl,
 #ifdef CONFIG_COMPAT