ramips: fix image recipe for ASUS RT-N56U
The OpenWrt image metadata includes checksum validation. Therefore,
it must be generated at the end.
Fixes: https://github.com/openwrt/openwrt/issues/9045
Fixes: https://github.com/openwrt/openwrt/issues/13674
Link: https://patchwork.ozlabs.org/project/openwrt/patch/TYCP286MB08952FAACDFA234C5E052131BCD82@TYCP286MB0895.JPNP286.PROD.OUTLOOK.COM/
Signed-off-by: Shiji Yang <[email protected]>
Shiji Yang