The rootfs is padded to the full block size by padjffs2 and a 4 byte magic
value ("deadc0de") is added to the end. On first boot, the JFFS2 is
replacing the "deadc0de" marker when the rootfs_data is initialized.
The static part of the rootfs is therefore $rootfs_size - 4 and not
$rootfs_size - 262144 - 4.
Signed-off-by: Sven Eckelmann <sven@narfation.org>