Since this is using Analysis Services as the source this would be better off done in the dataset unless you had a reason to be doing it in the report?

An MDX filter expression could be used against he date hierarchy could be used. E.g.

Ancestor(StrToMember("[Date].[Calendar].[Date].&[" + Format(Now(),"yyyyMMdd") + "]", CONSTRAINED), [Date].[Calendar].[Calendar Quarter]).Lag(1)