init dma mrpc output buffer to 0xff

In dma mrpc case, FW just push the valid length of data
to the dma buffer, which will lead to uninitialized data
after the valid data copy to userspace.

Author: wesleywesley

switchtec.c

@@ -143,6 +143,7 @@ static void mrpc_cmd_submit(struct switchtec_dev *stdev)
 
 	if (stdev->dma_mrpc) {
 		stdev->dma_mrpc->status = SWITCHTEC_MRPC_STATUS_INPROGRESS;
+		memset(stdev->dma_mrpc->data, 0xFF, SWITCHTEC_MRPC_PAYLOAD_SIZE);
 	}
 
 	stuser_set_state(stuser, MRPC_RUNNING);