[Relay][AlterOp] Minor refactor. (#4064)

src/relay/pass/alter_op_layout.h

@@ -53,10 +53,10 @@ inline Layout AdjustSubordinateFactors(const Layout& src_layout, const Layout& o
   for (auto axis : src_layout->axes) {
     if (!LayoutAxis::Get(axis).IsPrimal()) {
       // 1) Find the corresponding dual axis
-      auto dual_axis = LayoutAxis::Get(axis).ToPrimal().name()[0];
+      const auto& dual_axis = LayoutAxis::Get(axis).ToPrimal();
 
       // 2) Find the index of this dual axis in old_layout
-      int old_axis = old_layout.IndexOf(LayoutAxis::Get(dual_axis));
+      int old_axis = old_layout.IndexOf(dual_axis);
 
       // 3) Find the shape of this index in old_shape
       auto shape_val = old_shape[old_axis];
@@ -72,7 +72,7 @@ inline Layout AdjustSubordinateFactors(const Layout& src_layout, const Layout& o
 
       // 4) b) If shape is not 1, retain the factor.
       if (!is_shape_one) {
-        auto new_shape_val = src_layout.FactorOf(LayoutAxis::Get(dual_axis));
+        auto new_shape_val = src_layout.FactorOf(dual_axis);
         new_layout += std::to_string(new_shape_val);
       }
     }