build_doc: Fix minor warnings reported by pylint

  C: 88,4:handle_extra_module_doc_build: Comma not followed by a space
    raw_name_extra_module_src_package = extra_module_src_package_uri.rsplit('/',1)[-1] # get last item from array
                                                                               ^^
  C: 97,4:handle_extra_module_doc_build: Comma not followed by a space
    raw_name_qt5_bin_package = extra_module_doc_build_qt5_package_uri.rsplit('/',1)[-1] # get last item from array
                                                                                ^^
  C:106,4:handle_extra_module_doc_build: Comma not followed by a space
    raw_name_qt5_icu_package = extra_module_doc_build_qt5_icu_package_uri.rsplit('/',1)[-1] # get last item from array
                                                                                    ^^
Change-Id: I870e9ee53466599b7a350bec142bf1848560bfb2
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>