[X86] ISD::INSERT_SUBVECTOR - use uint64_t index. NFCI.
[X86] ISD::INSERT_SUBVECTOR - use uint64_t index. NFCI.

Keep the uint64_t type from getConstantOperandVal to stop truncation/extension overflow warnings in MSVC in subvector index math.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@365328 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm