[CVP] Fix assertion failure on vector with.overflow

[CVP] Fix assertion failure on vector with.overflow

Noticed on D62703. LVI only handles plain integers, not vectors of
integers. This was previously not an issue, because vector support
for with.overflow is only a relatively recent addition.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@362261 91177308-0d34-0410-b5e6-96231b3b80d8