fix compile error for Spark 3.2

gluten-core/src/main/scala/io/glutenproject/extension/MergeTwoPhasesHashAggregate.scala

@@ -50,7 +50,7 @@ case class MergeTwoPhasesHashBaseAggregate(session: SparkSession) extends Rule[S
             agg.groupingExpressions,
             agg.aggregateExpressions,
             agg.aggregateAttributes,
-            agg.initialInputBufferOffset,
+            0, // there is no field initialInputBufferOffset in Spark 3.2
             agg.resultExpressions,
             agg.child
           )