[MINOR] Correct LogisticRegression test case for probability2prediction.

## What changes were proposed in this pull request?
Set correct column names for ```force to use probability2prediction``` in ```LogisticRegressionSuite```.

## How was this patch tested?
Change unit test.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #16477 from yanboliang/lor-pred.

mllib/src/test/scala/org/apache/spark/ml/classification/LogisticRegressionSuite.scala

@@ -360,7 +360,7 @@ class LogisticRegressionSuite
     }
 
     // force it to use raw2prediction
-    model.setProbabilityCol("")
+    model.setRawPredictionCol("rawPrediction").setProbabilityCol("")
     val resultsUsingRaw2Predict =
       model.transform(smallMultinomialDataset).select("prediction").as[Double].collect()
     resultsUsingRaw2Predict.zip(results.select("prediction").as[Double].collect()).foreach {
@@ -368,7 +368,7 @@ class LogisticRegressionSuite
     }
 
     // force it to use probability2prediction
-    model.setRawPredictionCol("")
+    model.setRawPredictionCol("").setProbabilityCol("probability")
     val resultsUsingProb2Predict =
       model.transform(smallMultinomialDataset).select("prediction").as[Double].collect()
     resultsUsingProb2Predict.zip(results.select("prediction").as[Double].collect()).foreach {
@@ -414,7 +414,7 @@ class LogisticRegressionSuite
     }
 
     // force it to use raw2prediction
-    model.setProbabilityCol("")
+    model.setRawPredictionCol("rawPrediction").setProbabilityCol("")
     val resultsUsingRaw2Predict =
       model.transform(smallBinaryDataset).select("prediction").as[Double].collect()
     resultsUsingRaw2Predict.zip(results.select("prediction").as[Double].collect()).foreach {
@@ -422,7 +422,7 @@ class LogisticRegressionSuite
     }
 
     // force it to use probability2prediction
-    model.setRawPredictionCol("")
+    model.setRawPredictionCol("").setProbabilityCol("probability")
     val resultsUsingProb2Predict =
       model.transform(smallBinaryDataset).select("prediction").as[Double].collect()
     resultsUsingProb2Predict.zip(results.select("prediction").as[Double].collect()).foreach {