Fix dataflow bug in spmv products
Fix dataflow bug in spmv products

Any updates to x in [y = A * x] should come after y is computed.

dondieselkopf/amgcl,ddemidov/amgcl,huahbo/amgcl,huahbo/amgcl,ddemidov/amgcl,huahbo/amgcl,ddemidov/amgcl,ddemidov/amgcl,dondieselkopf/amgcl,dondieselkopf/amgcl