Revert "virtio-console: remove unnecessary kmemdup()"

This reverts commit 9db81eca10ba2d84177fa076704db3a5d76863c3.

A dependant patch on this one needs to be reverted, so this one also
needs to be reverted at this point in time.

Link: https://lore.kernel.org/r/[e-mail]
Reported-by: Jiri Slaby <[e-mail]>
Cc: Xianting Tian <[e-mail]>
Cc: Shile Zhang <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/char/virtio_console.c

···
 {
 	struct port *port;
 	struct scatterlist sg[1];
+	void *data;
+	int ret;
 
 	if (unlikely(early_put_chars))
 		return early_put_chars(vtermno, buf, count);
···
 	if (!port)
 		return -EPIPE;
 
-	sg_init_one(sg, buf, count);
-	return __send_to_port(port, sg, 1, count, (void *)buf, false);
+	data = kmemdup(buf, count, GFP_ATOMIC);
+	if (!data)
+		return -ENOMEM;
+
+	sg_init_one(sg, data, count);
+	ret = __send_to_port(port, sg, 1, count, data, false);
+	kfree(data);
+	return ret;
 }
 
 /*