[tint] Remove current_function from ValidateReturn.

The current_function was used to retrieve the functions return type.
Pass it in directly instead of using current_function.

Bug: tint:1313
Change-Id: Ie29407aecc51e8453460f46437b5c011088c3749
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/87145
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/tint/resolver/resolver.cc

@@ -2507,7 +2507,7 @@ sem::Statement* Resolver::ReturnStatement(const ast::ReturnStatement* stmt) {
 
     // Validate after processing the return value expression so that its type
     // is available for validation.
-    return ValidateReturn(stmt);
+    return ValidateReturn(stmt, current_function_->ReturnType());
   });
 }
 

src/tint/resolver/resolver.h

@@ -280,7 +280,8 @@ class Resolver {
   bool ValidateFunctionParameter(const ast::Function* func,
                                  const sem::Variable* var);
   bool ValidateParameter(const ast::Function* func, const sem::Variable* var);
-  bool ValidateReturn(const ast::ReturnStatement* ret);
+  bool ValidateReturn(const ast::ReturnStatement* ret,
+                      const sem::Type* func_type);
   bool ValidateStatements(const ast::StatementList& stmts);
   bool ValidateStorageTexture(const ast::StorageTexture* t);
   bool ValidateStructure(const sem::Struct* str, ast::PipelineStage stage);

src/tint/resolver/resolver_validation.cc

@@ -2181,9 +2181,8 @@ bool Resolver::ValidateLocationAttribute(
   return true;
 }
 
-bool Resolver::ValidateReturn(const ast::ReturnStatement* ret) {
-  auto* func_type = current_function_->ReturnType();
-
+bool Resolver::ValidateReturn(const ast::ReturnStatement* ret,
+                              const sem::Type* func_type) {
   auto* ret_type = ret->value ? TypeOf(ret->value)->UnwrapRef()
                               : builder_->create<sem::Void>();