firmware: imx: scu: Fix corruption of header

The header of the message to send can be changed if the
response is longer than the request:
 - 1st word, the header is sent
 - the remaining words of the message are sent
 - the response is received asynchronously during the
   execution of the loop, changing the size field in
   the header
 - the for loop test the termination condition using
   the corrupted header

It is the case for the API build_info which has just a
header as request but 3 words in response.

This issue is fixed storing the header locally instead of
using a pointer on it.

Fixes: edbee095 (firmware: imx: add SCU firmware driver support)
Signed-off-by: Franck LENORMAND <franck.lenormand@nxp.com>
Reviewed-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Cc: stable@vger.kernel.org
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

drivers/firmware/imx/imx-scu.c

@@ -158,7 +158,7 @@ static void imx_scu_rx_callback(struct mbox_client *c, void *msg)
 
 static int imx_scu_ipc_write(struct imx_sc_ipc *sc_ipc, void *msg)
 {
-	struct imx_sc_rpc_msg *hdr = msg;
+	struct imx_sc_rpc_msg hdr = *(struct imx_sc_rpc_msg *)msg;
 	struct imx_sc_chan *sc_chan;
 	u32 *data = msg;
 	int ret;
@@ -166,13 +166,13 @@ static int imx_scu_ipc_write(struct imx_sc_ipc *sc_ipc, void *msg)
 	int i;
 
 	/* Check size */
-	if (hdr->size > IMX_SC_RPC_MAX_MSG)
+	if (hdr.size > IMX_SC_RPC_MAX_MSG)
 		return -EINVAL;
 
-	dev_dbg(sc_ipc->dev, "RPC SVC %u FUNC %u SIZE %u\n", hdr->svc,
-		hdr->func, hdr->size);
+	dev_dbg(sc_ipc->dev, "RPC SVC %u FUNC %u SIZE %u\n", hdr.svc,
+		hdr.func, hdr.size);
 
-	size = sc_ipc->fast_ipc ? 1 : hdr->size;
+	size = sc_ipc->fast_ipc ? 1 : hdr.size;
 	for (i = 0; i < size; i++) {
 		sc_chan = &sc_ipc->chans[i % 4];