TableGen: Fix type of resolved and converted lists

Summary:
There are no new test cases, but a subsequent patch will introduce
assertions that would be triggered by existing test cases without this
fix.

Change-Id: I6a82d4b311b012aff3932978ae86f6a2dcfbf725

Reviewers: arsenm, craig.topper, tra, MartinO

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D43556

llvm-svn: 325798