You are adding package source feed to binary feed. Opkg requires compiled packages. Git you have contains just a makefiles not a compiled packages. You want to use something like this http://downloads.lede-project.org/releases/17.01.2/targets/ramips/rt305x/packages (of course not this one as this is different cpu architecture and such).
But overall you shouldn’t be doing that as packages in OpenWRT/Lede repository are compiled against different base system (libraries and compiler versions) and expect slightly different environment (some scripts on Turris are based on OpenWRT with our changes but Lede did its own changes and as such we can’t ensure compatibility). Overall it’s a bad bad idea. If you need some package that we don’t provide than you should either request it from us or build it on your own against our sdk (http://repo.turris.cz/omnia/OpenWrt-SDK-mvebu_gcc-4.8-linaro_musl-1.1.15_eabi.Linux-x86_64.tar.bz2)