[x86] Fix register class of folded load index reg.

[x86] Fix register class of folded load index reg.

When folding a load in to another instruction, we need to fix the class of the index register
Otherwise, it could be something like GR64 not GR64_NOSP and would fail the machine verifier.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236644 91177308-0d34-0410-b5e6-96231b3b80d8