scripts/gen_image_generic.sh: fail on errors

The script always exits with value 0, even if some of the commands fail.
This can potentially create broken, unbootable images, e.g. when
make_ext4fs fails due to TARGET_KERNEL_PARTSIZE being too small for the
kernel. Avoid this by failing the script when any command fails.

Acked-by: Jo-Philipp Wich <jo@mein.io>
Acked-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

scripts/gen_image_generic.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 # Copyright (C) 2006-2012 OpenWrt.org
-set -x
+set -e -x
 [ $# == 5 -o $# == 6 ] || {
     echo "SYNTAX: $0 <file> <kernel size> <kernel directory> <rootfs size> <rootfs image> [<align>]"
     exit 1