[X86] Use MVT::getVectorVT instead of EVT::getVectorVT when splitting 256/512 bit build_vectors. NFC

We must be creating a legal type here which means it can be an MVT.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322512 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed