[CODEGEN] Change return type of generator::packed_type to appease build warnings (#507)

include/triton/codegen/selection/generator.h

@@ -116,7 +116,7 @@ private:
 private:
   Type *cvt(ir::type *ty);
   llvm::Attribute cvt(ir::attribute attr);
-  llvm::StructType* packed_type(ir::value* i);
+  void packed_type(ir::value* i);
   void forward_declare(ir::function* fn);
 
 public:

lib/codegen/selection/generator.cc

@@ -3326,7 +3326,7 @@ void generator::finalize_phi_node(ir::phi_node *x) {
   }
 }
 
-StructType* generator::packed_type(ir::value* i){
+void generator::packed_type(ir::value* i){
   Type* dtype = cvt(i->get_type()->get_tile_element_ty());
   auto* layout = dynamic_cast<analysis::scanline_layout*>(layouts_->get(i));
   assert(layout);