[SPARK-24160][FOLLOWUP] Fix compilation failure

## What changes were proposed in this pull request?

SPARK-24160 is causing a compilation failure (after SPARK-24143 was merged). This fixes the issue.

## How was this patch tested?

building successfully

Author: Marco Gaido <[email protected]>

Closes #21256 from mgaido91/SPARK-24160_FOLLOWUP.

Author: mgaido91

core/src/test/scala/org/apache/spark/storage/ShuffleBlockFetcherIteratorSuite.scala

@@ -546,7 +546,7 @@ class ShuffleBlockFetcherIteratorSuite extends SparkFunSuite with PrivateMethodT
       taskContext,
       transfer,
       blockManager,
-      blocksByAddress,
+      blocksByAddress.toIterator,
       (_, in) => in,
       48 * 1024 * 1024,
       Int.MaxValue,