[VPlan] Fix header phi VPInstruction verification. NFC#151472

lukel97 merged 4 commits intollvm:mainllvm/llvm-project:mainfrom

lukel97:loop-vectorize/fix-header-vpinstruction-phi-verifylukel97/llvm-project:loop-vectorize/fix-header-vpinstruction-phi-verifyCopy head branch name to clipboard