NFS: Fix a compile issue when CONFIG_NFS_V4_1 is undefined

struct nfs_direct_req can't compile when struct pnfs_ds_commit_info
is undefined.

Reported-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Fred Isaman <iisaman@netapp.com>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index c940d46..6deb8f0 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1176,6 +1176,11 @@
 	struct nfs4_sequence_res	seq_res;
 };
 
+#else
+
+struct pnfs_ds_commit_info {
+};
+
 #endif /* CONFIG_NFS_V4_1 */
 
 struct nfs_page;