sandbox: put stdin into raw mode

This allows us to act like a serial device: we get tab chars and CTRL+C
and respond appropriately.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/sandbox.c b/drivers/serial/sandbox.c
index 814a0f9..1927c16 100644
--- a/drivers/serial/sandbox.c
+++ b/drivers/serial/sandbox.c
@@ -30,6 +30,7 @@
 
 int serial_init(void)
 {
+	os_tty_raw(0);
 	return 0;
 }