https://openwrt.org/docs/techref/bootloader/uboot.config
>Some devices seem not to have the uboot_env section and the environment appears with an offset in the section containing uboot (/dev/mtd0) here.
>In the latter case expect that the environment address (offset) is a multiple of Flash sector size.
とのことでmtd0の中に入っている場合もあるようです