[SPARK-17586][BUILD] Do not call static member via instance reference

## What changes were proposed in this pull request?

This PR fixes a warning message as below:

```
[WARNING] .../UnsafeInMemorySorter.java:284: warning: [static] static method should be qualified by type name, TaskMemoryManager, instead of by an expression
[WARNING]       currentPageNumber = memoryManager.decodePageNumber(recordPointer)
```

by referencing the static member via class not instance reference.

## How was this patch tested?

Existing tests should cover this - Jenkins tests.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #15141 from HyukjinKwon/SPARK-17586.

1 files changed, 1 insertions, 1 deletions

diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeInMemorySorter.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeInMemorySorter.java
index be382955c0..3b1ece4373 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeInMemorySorter.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeInMemorySorter.java
@@ -281,7 +281,7 @@ public final class UnsafeInMemorySorter {
     public void loadNext() {
       // This pointer points to a 4-byte record length, followed by the record's bytes
       final long recordPointer = array.get(offset + position);
-      currentPageNumber = memoryManager.decodePageNumber(recordPointer);
+      currentPageNumber = TaskMemoryManager.decodePageNumber(recordPointer);
       baseObject = memoryManager.getPage(recordPointer);
       baseOffset = memoryManager.getOffsetInPage(recordPointer) + 4;  // Skip over record length
       recordLength = Platform.getInt(baseObject, baseOffset - 4);