NFS: Create a common results structure for reads and writes

Reads and writes have very similar results.  This patch combines the two
structs together with comments to show where the differing fields are
used.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 25ba383..d392a70 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1389,7 +1389,7 @@
 void nfs_writeback_done(struct rpc_task *task, struct nfs_write_data *data)
 {
 	struct nfs_pgio_args	*argp = &data->args;
-	struct nfs_writeres	*resp = &data->res;
+	struct nfs_pgio_res	*resp = &data->res;
 	struct inode		*inode = data->header->inode;
 	int status;