pNFS/flexfiles: Fix a statistics gathering imbalance

When we replay a failed read, write or commit to the dataserver, we
need to ensure that we call ff_layout_read_prepare_v3(),
ff_layout_write_prepare_v3 or ff_layout_commit_prepare_v3() so that we
reset the statistics.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -1130,7 +1130,7 @@ static int ff_layout_async_handle_error_v3(struct rpc_task *task,
 	return -NFS4ERR_RESET_TO_PNFS;
 out_retry:
 	task->tk_status = 0;
-	rpc_restart_call(task);
+	rpc_restart_call_prepare(task);
 	rpc_delay(task, NFS_JUKEBOX_RETRY_TIME);
 	return -EAGAIN;
 }