cubietech-cubieboard: fix u-boot dependency
Follow change in Alpine Linux: https://gitlab.alpinelinux.org/alpine/aports/-/commit/ac3bfe0e20536642baa2840ff394fa42987c7497
CC @DolphinChips
Follow change in Alpine Linux: https://gitlab.alpinelinux.org/alpine/aports/-/commit/ac3bfe0e20536642baa2840ff394fa42987c7497
CC @DolphinChips