tools: kwboot: Fix initializing tty device

Retrieve current terminal settings via tcgetattr(), set to raw mode with
cfmakeraw(), enable receiver via CREAD and ignore modem control lines
via CLOCAL.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/tools/kwboot.c b/tools/kwboot.c
index d8b9507..fc83161 100644
--- a/tools/kwboot.c
+++ b/tools/kwboot.c
@@ -648,11 +648,12 @@
 	if (fd < 0)
 		goto out;
 
-	memset(&tio, 0, sizeof(tio));
-
-	tio.c_iflag = 0;
-	tio.c_cflag = CREAD|CLOCAL|CS8;
+	rc = tcgetattr(fd, &tio);
+	if (rc)
+		goto out;
 
+	cfmakeraw(&tio);
+	tio.c_cflag |= CREAD|CLOCAL;
 	tio.c_cc[VMIN] = 1;
 	tio.c_cc[VTIME] = 10;