Fix SmallName for ParamTypeDType
based on the discussion here (https://github.com/ucb-bar/chisel3/pull/293) I found that type parameters lead to a problem with generated files and emitted code with -O0, because SmallNames did not set a character. Hence \000 was used, with the file name and content getting messed up.
The SmallName of type parameters needs to be generated, otherwise files/modules with character \000 were generated after calling paramSmallName.
With this patch the SmallName 'T' is used for type parameters.
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