platform/chrome: Fix locking pattern in wilco_ec_mailbox()

Before, ec->data_buffer could be written to from multiple
contexts at the same time. Since the ec is shared data,
it needs to be inside the mutex as well.

Fixes: 7b3d4f44 ("platform/chrome: Add new driver for Wilco EC")
Signed-off-by: Nick Crews <ncrews@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Benson Leung <bleung@chromium.org>

drivers/platform/chrome/wilco_ec/mailbox.c

@@ -223,11 +223,11 @@ int wilco_ec_mailbox(struct wilco_ec_device *ec, struct wilco_ec_message *msg)
 		msg->command, msg->type, msg->flags, msg->response_size,
 		msg->request_size);
 
+	mutex_lock(&ec->mailbox_lock);
 	/* Prepare request packet */
 	rq = ec->data_buffer;
 	wilco_ec_prepare(msg, rq);
 
-	mutex_lock(&ec->mailbox_lock);
 	ret = wilco_ec_transfer(ec, msg, rq);
 	mutex_unlock(&ec->mailbox_lock);