get_cache_size() does not modify cache_type so it could be const.

Mark cache_type const so that const char * can be passed to it. This
prevents warnings once many of the test parameters are marked const.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>