fix bug when generating event stream events serializer (smithy-lang#283)

Author: AllanZhengYP

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/integration/HttpBindingProtocolGenerator.java

@@ -1284,8 +1284,8 @@ private void writeEventBody(GenerationContext context, StructureShape event) {
             // Write event document bindings if exist.
             SymbolProvider symbolProvider = context.getSymbolProvider();
             Symbol symbol = symbolProvider.toSymbol(event);
-            // Use normal structure deserializer instead of event deserializer to deserialize document body.
-            String serFunctionName = ProtocolGenerator.getDeserFunctionName(symbol, context.getProtocolName());
+            // Use normal structure serializer instead of event serializer to serialize document body.
+            String serFunctionName = ProtocolGenerator.getSerFunctionName(symbol, context.getProtocolName());
             writer.write("message.body = $L(input, context);", serFunctionName);
         }
     }