scripts/om-fwupgradecfg-gen.sh: Fix u-boot image md5sum check

scripts/om-fwupgradecfg-gen.sh: Fix u-boot image md5sum check

The u-boot on Open Mesh devices checks the whole transfered image against a
md5sum. This is stored inside the option filemd5sum inside the
fwupgrade.cfg. The bootloader will not check it when this setting is
missing and could therefore write invalid images to the flash.

Signed-off-by: Sven Eckelmann <sven@open-mesh.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46925 3c298f89-4303-0410-b956-a3cf2f4a3e73