MINOR: Fix log statement formatting in KafkaAdminClient (#21990)

Fix log statement to use the local variable `defaultApiTimeoutMs`
instead of the uninitialized field `this.defaultApiTimeoutMs`.

Reviewers: Chia-Ping Tsai <chia7712@gmail.com>

Author: JiayaoS

clients/src/main/java/org/apache/kafka/clients/admin/KafkaAdminClient.java

@@ -657,7 +657,7 @@ private int configureDefaultApiTimeoutMs(AdminClientConfig config) {
                     " must be no smaller than the value of " + AdminClientConfig.REQUEST_TIMEOUT_MS_CONFIG + ".");
             } else {
                 log.warn("Overriding the default value for {} ({}) with the explicitly configured request timeout {}",
-                    AdminClientConfig.DEFAULT_API_TIMEOUT_MS_CONFIG, this.defaultApiTimeoutMs,
+                    AdminClientConfig.DEFAULT_API_TIMEOUT_MS_CONFIG, defaultApiTimeoutMs,
                     requestTimeoutMs);
                 return requestTimeoutMs;
             }