[SelectionDAG] Remove ISD::ADDC/ADDE from some undef handling code in getNode. NFCI

These nodes should have two results. A real VT and a Glue. But this code would have returned Undef which would only be a single result. But we're in the single result version of getNode so these opcodes should never be seen by this function anyway.

llvm-svn: 348670