Remove unused but set variable from prims_ll128.h (#1257)

Allows `-Wunused-but-set-variable` to pass

[ROCm/rccl commit: 86a4ad6e8b]

projects/rccl/src/device/prims_ll128.h

@@ -382,7 +382,6 @@ private:
 
     T const *srcPtr = srcs[0];
     T       *dstPtr = dsts[0];
-    int wireOffset = WireWordPerSlice*warp + 2*wid;
     const int nwarps = nthreads/WARP_SIZE;
     nelem = nelem < 0 ? 0 : nelem;
 
@@ -438,7 +437,6 @@ private:
         }
       }
 
-      wireOffset += WireWordPerSlice*nwarps;
       srcPtr += DataEltPerSlice*nwarps;
       dstPtr += DataEltPerSlice*nwarps;
       if (MULTISRCS){
@@ -580,4 +578,4 @@ public:
   __device__ void localCopy(T* srcs, T* dsts, int eltN) {
     return mscclGenericOp<0,1,0,0>(&srcs, 1, &dsts, 1, eltN);
   }
-};
+};