NFS: Replace file->private_data with calls to nfs_file_open_context()

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 51e4a77..5c200fd 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -338,12 +338,8 @@
 
 static inline struct rpc_cred *nfs_file_cred(struct file *file)
 {
-	if (file != NULL) {
-		struct nfs_open_context *ctx;
-
-		ctx = (struct nfs_open_context*)file->private_data;
-		return ctx->cred;
-	}
+	if (file != NULL)
+		return nfs_file_open_context(file)->cred;
 	return NULL;
 }