pNFS: Cleanup - don't open code pnfs_mark_layout_stateid_invalid()

Ensure nfs42_layoutstat_done() layoutget don't open code layout stateid
invalidation.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index 2f4f269..d71c949 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -268,6 +268,8 @@
 				struct list_head *tmp_list,
 				const struct pnfs_layout_range *recall_range,
 				u32 seq);
+int pnfs_mark_layout_stateid_invalid(struct pnfs_layout_hdr *lo,
+		struct list_head *lseg_list);
 bool pnfs_roc(struct inode *ino);
 void pnfs_roc_release(struct inode *ino);
 void pnfs_roc_set_barrier(struct inode *ino, u32 barrier);