[MINOR][SPARKR] Fix arguments of survreg in SparkR

## What changes were proposed in this pull request?
Fix wrong arguments description of ```survreg``` in SparkR.

## How was this patch tested?
```Arguments``` section of ```survreg``` doc before this PR (with wrong description for ```path``` and missing ```overwrite```):
![image](https://cloud.githubusercontent.com/assets/1962026/16447548/fe7a5ed4-3da1-11e6-8b96-b5bf2083b07e.png)

After this PR:
![image](https://cloud.githubusercontent.com/assets/1962026/16447617/368e0b18-3da2-11e6-8277-45640fb11859.png)

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #13970 from yanboliang/spark-16143-followup.

R/pkg/R/mllib.R

@@ -442,11 +442,11 @@ setMethod("write.ml", signature(object = "NaiveBayesModel", path = "character"),
 
 # Saves the AFT survival regression model to the input path.
 
-#' @param path The directory where the model is savedist containing the model's coefficien
+#' @param path The directory where the model is saved
+#' @param overwrite Overwrites or not if the output path already exists. Default is FALSE
 #'                  which means throw exception if the output path exists.
 #'
 #' @rdname spark.survreg
-#' @name write.ml
 #' @export
 #' @note write.ml(AFTSurvivalRegressionModel, character) since 2.0.0
 #' @seealso \link{read.ml}