x86/resctrl: Remove redundant variable in mbm_config_write_domain()

The kernel test robot reported the following warning after commit

  54e35eb8 ("x86/resctrl: Read supported bandwidth sources from CPUID").

even though the issue is present even in the original commit

  92bd5a13 ("x86/resctrl: Add interface to write mbm_total_bytes_config")

which added this function. The reported warning is:

  $ make C=1 CHECK=scripts/coccicheck arch/x86/kernel/cpu/resctrl/rdtgroup.o
  ...
  arch/x86/kernel/cpu/resctrl/rdtgroup.c:1621:5-8: Unneeded variable: "ret". Return "0" on line 1655

Remove the local variable 'ret'.

  [ bp: Massage commit message, make mbm_config_write_domain() void. ]

Fixes: 92bd5a13

 ("x86/resctrl: Add interface to write mbm_total_bytes_config")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401241810.jbd8Ipa1-lkp@intel.com/
Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/r/202401241810.jbd8Ipa1-lkp@intel.com