[rocketmq]fix variable judgment bug

spring-cloud-alibaba-starters/spring-cloud-starter-stream-rocketmq/src/main/java/com/alibaba/cloud/stream/binder/rocketmq/config/RocketMQComponent4BinderAutoConfiguration.java

@@ -74,7 +74,7 @@ public class RocketMQComponent4BinderAutoConfiguration {
 			configNameServer = RocketMQBinderConstants.DEFAULT_NAME_SERVER;
 		}
 		producer.setNamesrvAddr(configNameServer);
-		if (!StringUtils.isEmpty(configNameServer)) {
+		if (!StringUtils.isEmpty(accessChannel)) {
 			producer.setAccessChannel(AccessChannel.valueOf(accessChannel));
 		}
 		return producer;