[DAGCombiner] `visitFREEZE()`: gracefully handle node invalidation

When we freeze operands of an operation that we are trying to freeze,
doing so may invalidate the original SDValue. We should just re-fetch
it from the ISD::FREEZE node, because if we bail, we'd hopefully just
revisit the node and do that again.

Fixes https://github.com/llvm/llvm-project/issues/59891

Differential Revision: https://reviews.llvm.org/D141256