pNFS/flexfiles: Minor refactoring before adding iostats to layoutreturn

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index b64177d..617cfaa 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -357,8 +357,7 @@ struct nfs42_layoutstat_devinfo {
 	__u64 write_count;
 	__u64 write_bytes;
 	__u32 layout_type;
-	layoutstats_encode_t layoutstats_encode;
-	void *layout_private;
+	struct nfs4_xdr_opaque_data ld_private;
 };
 
 struct nfs42_layoutstat_args {