[AMDGPU] Fix for the lost CarryOut/CarryIn register operands in S_ADD/SUB_CO_PSEUDO.

Summary: This fixes the 5b898bdd bug when the carry-in and carry-out registers became lost in lowering S_ADD/SUB_CO_PSEUDO.

Reviewers: rampitec, arsenm

Reviewed By: arsenm

Subscribers: msearles, arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, kerbowa, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80158