staging/mei: don't use read buffer for writing

In mei_irq_thread_read_bus_message we reused mei_hdr
allocated on read buffer to write the stop message.
There is no bug associated with this but for code
clarity we use write buffer also for message header.
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mei/interrupt.c

@@ -652,6 +652,7 @@ static void mei_irq_thread_read_bus_message(struct mei_device *dev,
 		} else {
 			dev->version = version_res->me_max_version;
 			/* send stop message */
+			mei_hdr = (struct mei_msg_hdr *)&dev->wr_msg_buf[0];
 			mei_hdr->host_addr = 0;
 			mei_hdr->me_addr = 0;
 			mei_hdr->length = sizeof(struct hbm_host_stop_request);