Fix an amusing typo that completely the re-introduction of parameters

Fix an amusing typo that completely the re-introduction of parameters
for the purposes of parsing default arguments. In effect, we would
re-introduce the parameter with a default argument N times (where N is
the number of parameters preceding the parameter with a default
argument). This showed up when a defaulted parameter of a member
function of a local class shadowed a parameter of the enclosing
function. Fixes PR6383.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@97534 91177308-0d34-0410-b5e6-96231b3b80d8