[SPARK-11746][CORE] Use cache-aware method dependencies

a small change

Author: hushan <hushan@xiaomi.com>

Closes #9691 from suyanNone/unify-getDependency.

core/src/main/scala/org/apache/spark/rdd/PartitionPruningRDD.scala

@@ -65,7 +65,7 @@ class PartitionPruningRDD[T: ClassTag](
   }
 
   override protected def getPartitions: Array[Partition] =
-    getDependencies.head.asInstanceOf[PruneDependency[T]].partitions
+    dependencies.head.asInstanceOf[PruneDependency[T]].partitions
 }