[DAGCombiner] Use HandleSDNode to keep node alive across call to getNegatedExpression.

getNegatedExpression can delete nodes. If the first call to
getNegatedExpression produced a node that the second call also
manages to create, it might get deleted. Use a HandleSDNode to
ensure it has a use to prevent it from being deleted.

Fixes PR57658.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D133602