[SPARK-16120][STREAMING] getCurrentLogFiles in ReceiverSuite WAL generating...

[SPARK-16120][STREAMING] getCurrentLogFiles in ReceiverSuite WAL generating and cleaning case uses external variable instead of the passed parameter

## What changes were proposed in this pull request?

In `ReceiverSuite.scala`, in the test case "write ahead log - generating and cleaning", the inner method `getCurrentLogFiles` uses external variable `logDirectory1` instead of the passed parameter `logDirectory`. This PR fixes this by using the passed method argument instead of variable from the outer scope.

## How was this patch tested?

The unit test was re-run and the output logs were checked for the correct paths used.

tdas

Author: Ahmed Mahran <ahmed.mahran@mashin.io>

Closes #13825 from ahmed-mahran/b-receiver-suite-wal-gen-cln.

streaming/src/test/scala/org/apache/spark/streaming/ReceiverSuite.scala

@@ -215,7 +215,7 @@ class ReceiverSuite extends TestSuiteBase with Timeouts with Serializable {
     def getCurrentLogFiles(logDirectory: File): Seq[String] = {
       try {
         if (logDirectory.exists()) {
-          logDirectory1.listFiles().filter { _.getName.startsWith("log") }.map { _.toString }
+          logDirectory.listFiles().filter { _.getName.startsWith("log") }.map { _.toString }
         } else {
           Seq.empty
         }