This commit prevents the variable "_module" from being overwritten
in vtk_module_config() after being set in "pv_process_modules()".

In the particular project where the error was investigated, it fixes
a failure to link the plugin against wslink and wslinkCS.

The pseudo code reported below illustrates the scenario leading to
the link error:

//-----------------------------
pv_process_modules()                                          [/path/to/Plugins/<NameOfPlugin>/CMakeLists.txt]
  -> foreach(_module IN LISTS current_module_set_sorted)      [ParaViewPlugins.cmake         :pv_process_modules]
     ############################################################################################################
     # NOTE: _module is set here
     ############################################################################################################
     [...]
     -> vtk_add_cs_wrapping(${_module})                       [ParaViewPlugin...