Fix using wrong result type for setcc.

When reducing the bitwidth of a comparison against a constant, the
original setcc's result type was used, which was incorrect.

No test since I don't think any other in tree targets change the
bitwidth of the setcc type depending on the bitwidth of the compared
type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208236 91177308-0d34-0410-b5e6-96231b3b80d8