libostree: Make introspectable again
libostree: Make introspectable again

At some point, the variable name for the headers changed and the
introspection build line forgot to be updated.

https://bugzilla.gnome.org/show_bug.cgi?id=707228

sujitfulse/ostree,leandrosansilva/ostree,gatispaeglis/ostree,gatispaeglis/ostree,resin-io/ostree,leandrosansilva/ostree,GNOME/ostree,sujitfulse/ostree,resin-io/ostree,GNOME/ostree,GNOME/ostree,sujitfulse/ostree,sujitfulse/ostree,gatispaeglis/ostree,gatispaeglis/ostree,resin-io/ostree,gatispaeglis/ostree,leandrosansilva/ostree,GNOME/ostree,resin-io/ostree,leandrosansilva/ostree,sujitfulse/ostree,gatispaeglis/ostree,leandrosansilva/ostree,GNOME/ostree,resin-io/ostree