[LLVM] convergence verifier should visit all instructions (#66200)

The entry and loop intrinsics for convergence control cannot be preceded
by convergent operations in their respective basic blocks. To check
that, the verifier needs to reset its state at the start of the block.
This was missed in the previous commit
fa6dd7a24af2b02f236ec3b980d9407e86c2c4aa.