update TODO
bus: move attribute to end of structure, so it is not ignored

src/libsystemd-bus/bus-message.h:41:1: warning: attribute 'packed' is ignored, place it after
      "struct" to apply attribute to type declaration [-Wignored-attributes]
bus: don't free an unallocated var

Also remove unused variable.
udevadm: place const in the right place

Otherwise clang at least thinks that both consts apply to char.