I'm pretty sure it would be the 'high commission of ghana in berlin' or the embassy for ghana in berlin or whoever it was that issued the passport. If you're not comfortable calling a bunch of random authorities to find out, just email/call your uni's international student office and they'll be able to help.
EDIT: just fyi, the issuing authority is DEFINITELY not just 'the republic of ghana'. It's the city/country/centre where your passport was issued. it helps them distinguish between someone who has a passport issued in their home country, and someone who has a passport from a certain country that was issued in another country.