[SPARK-20098][PYSPARK] dataType's typeName fix

## What changes were proposed in this pull request?
`typeName`  classmethod has been fixed by using type -> typeName map.

## How was this patch tested?
local build

Author: Peter Szalai <szalaipeti.vagyok@gmail.com>

Closes #17435 from szalai1/datatype-gettype-fix.