TargetLowering: Fix off-by-one error

This problem was present for a while, but somehow asan didn't catch
it before the refactoring in r321036.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321043 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed