how to order my tuple of spark results descending order using value

You have almost done it! you need add additional parameter for descending order as RDD sortBy() method arrange elements in ascending order by default.

val results = ratings.countByValue()
val sortedRdd = results.sortBy(_._2, false)

//Just to display results from RDD
println(sortedRdd.collect().toList)

You can use

.sortWith(_._2 >_._2)

most of the time calling toSeq is not good idea because driver needs to put this in memory and you might run out of memory in on larger data sets. I guess this is o.k. for intro to spark.