UPSC Civil Service Examination is aimed at selecting administrators for various departments of Government of India. An administrator is supposed to be a generalist who can take decisions based on the advice given by specialist rather than a specialist himself.
Hence there is no educational qualification specified for UPSC rather than one needs to be 21 years old and must be a graduate from a recognised university. Since UPSC has not specified any particular educational qualification, it is evident that there is no specific advantage, your undergraduate degree can give you.
However, when it comes to subjects that one has to prepare for UPSC CSE, students who have taken subjects such as History or Geography may find an advantage in the initial stages of preparation.
This advantage can be overcome by dedicated students since the General Studies paper expects answers in the level of a student who has just completed his 12th std examination.
The only real advantage when it comes to education stream is in the selection of optional, since UPSC expects the answers of your optional to be in the level of Honour’s degree.
Hence, those who have studied their optional subject in their undergraduate level will have an easier time studying the optional subjects.
This too can be overcome with effective coaching and smartly choosing your optional paper.