[ir] Builder::Return takes single Value

Return instructions have at most one value, so we don't need to pass
in a whole utils::Vector to the builder method.

Bug: tint:1718
Change-Id: I61a4edc3ee2a50fc805b65f3e5fdc7538e7383a8
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/136781
Kokoro: Kokoro <noreply+kokoro@google.com>
Auto-Submit: James Price <jrprice@google.com>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
diff --git a/src/tint/ir/builder.h b/src/tint/ir/builder.h
index 57144a8..7c87272 100644
--- a/src/tint/ir/builder.h
+++ b/src/tint/ir/builder.h
@@ -343,9 +343,9 @@
 
     /// Creates a return instruction
     /// @param func the function being returned
-    /// @param args the return arguments
+    /// @param value the return value
     /// @returns the instruction
-    ir::Return* Return(Function* func, utils::VectorRef<Value*> args = utils::Empty);
+    ir::Return* Return(Function* func, Value* value = nullptr);
 
     /// Creates a loop next iteration instruction
     /// @param loop the loop being iterated