I’m afraid nobody can fix this, except HBO itself. My guess is that they still use Silverlight, even though Microsoft dropped the development a few years ago. It turned out not to be safe, but most big streaming and cable providers already invested in the silverlight technology. Now most companies like HBO must invest to change the technology into html5 and that is a new investment for them. Not only do they have to change the platform, but they have to pay the copyright fees for series and movies again.
Untill that is solved, HBO go will not be available for Linux. Just be patient, over here in The Netherlands we had the same issue with a big TV provider, but since last week (after two years of promises and waiting) their streaming content is available for all platforms.
Everybody is a genius, but if you judge a fish by its ability to climb a tree, it will live its whole life believing its stupid.