selftests/resctrl: Move ->setup() call outside of test specific branches

resctrl_val() function is called only by MBM, MBA, and CMT tests which
means the else branch is never used.

Both test branches call param->setup().

Remove the unused else branch and place the ->setup() call outside of
the test specific branches reducing code duplication.

Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
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>