[llvm] [SDAG] Disable illegal extract_subvector splitting for scalable vectors (PR #170315)

[Shunsuke Watanabe via llvm-commits]

https://github.com/s-watanabe314 approved this pull request.

Thank you for the patch! I'm not familiar with the code, so I can't review it, but I've confirmed that the test I mentioned now pass.

https://github.com/llvm/llvm-project/pull/170315