tools: kwboot: Fix initialization of tty device

Explicitly disable 2 stop bits by clearing CSTOPB flag, disable modem
control flow by clearing CRTSCTS flag and do not send hangup after closing
device by clearing HUPCL flag.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>

tools/kwboot.c

@@ -657,6 +657,7 @@ kwboot_open_tty(const char *path, int baudrate)
 
 	cfmakeraw(&tio);
 	tio.c_cflag |= CREAD | CLOCAL;
+	tio.c_cflag &= ~(CSTOPB | HUPCL | CRTSCTS);
 	tio.c_cc[VMIN] = 1;
 	tio.c_cc[VTIME] = 0;