R600/SI: Fix bitcast between v2i32 and f64

This is the same problem fixed in r210664 for more types.

The test passes without this fix. For some reason
I'm only hitting this when creating selects lowered
to v2i32 selects.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210692 91177308-0d34-0410-b5e6-96231b3b80d8