Fixed a glitch in &dch, which removed the flops.

src/aig/dch/dchChoice.c

@@ -463,6 +463,7 @@ Aig_Man_t * Dch_DeriveChoiceAigInt( Aig_Man_t * pAig )
     Aig_ManForEachPo( pAig, pObj, i )
         Aig_ObjCreatePo( pChoices, Aig_ObjChild0CopyRepr(pChoices, pObj) );
     Dch_DeriveChoiceCountEquivs( pChoices );
+    Aig_ManSetRegNum( pChoices, Aig_ManRegNum(pAig) );
     return pChoices;
 }