qdoc: Match unqualified parameter types

clangqdoc was unable to tie qdoc comments to their
function declarations for nested classes, when the
function had a formal parameter of the nested class
type. The problem was that findNodeForCursor() didn't
handle the type name scoping correctly.

Change-Id: I64d81377193447b1af73ecd107f0431fac0d81a7
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>