NFS: Create a common pgio_rpc_prepare function

The read and write paths do exactly the same thing for the rpc_prepare
rpc_op.  This patch combines them together into a single function.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index 5948125..da00a4d 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -53,8 +53,10 @@
 };
 
 struct nfs_rw_ops {
+	const fmode_t rw_mode;
 	struct nfs_rw_header *(*rw_alloc_header)(void);
 	void (*rw_free_header)(struct nfs_rw_header *);
+	void (*rw_release)(struct nfs_pgio_data *);
 };
 
 struct nfs_pageio_descriptor {