[llvm] [SLP] NFC. Use InstructionsState::valid if users just want to know whether VL has same opcode. (PR #120217)

[Han-Kuan Chen via llvm-commits]

HanKuanChen wrote:

> Looks like this has been crashing for a couple of hours.
> 
> Can we revert this to unblock people or land a fix ASAP?

It is fixed by https://github.com/llvm/llvm-project/pull/122443.

https://github.com/llvm/llvm-project/pull/120217