fix sgd for SelectedRows bug

paddle/fluid/operators/sgd_op.h

@@ -96,8 +96,12 @@ class SGDOpKernel : public framework::OpKernel<T> {
         return;
       }
 
-      size_t param_row_width = param.value().numel() / param.rows().size();
-      size_t grad_row_width = grad.value().numel() / grad.rows().size();
+      auto param_row_width = param.value().dims()[1];
+      auto grad_row_width = grad.value().dims()[1];
+      VLOG(4) << " param rows: " << param.rows().size()
+              << " param memory rows: " << param.value().dims()[0]
+              << " grad rows: " << grad.rows().size()
+              << " grad memory rows: " << grad.value().dims()[0];
       PADDLE_ENFORCE_EQ(param_row_width, grad_row_width,
                         "param_row should have the same size with grad_row");