[PATCH v2] x86/resctrl: Fix 'uninitialized symbol' build warning

[Babu Moger <babu.moger@amd.com>]

The recent commit 064855a69003 ("x86/resctrl: Fix default monitoring
groups reporting"), caused a RHEL build failure with an uninitialized
variable warning treated as an error. The commit removed the default case
snippet. The RHEL Makefile uses '-Werror=maybe-uninitialized' to force
uninitialized variable warnings to be treated as errors. This is also
reported by kernel test robot. The error from the RHEL build is below:

arch/x86/kernel/cpu/resctrl/monitor.c: In function ‘__mon_event_count’:
arch/x86/kernel/cpu/resctrl/monitor.c:261:12: error: ‘m’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
  m->chunks += chunks;
            ^~

The upstream Makefile does not build using '-Werror=maybe-uninitialized'.
So, the problem is not seen there. Fix the problem by putting back the
default case snippet.

Fixes: 064855a69003 ("x86/resctrl: Fix default monitoring groups reporting")
Cc: stable@vger.kernel.org
Reported-by: Terry Bowman <Terry.Bowman@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/lkml/6118d218.4ZZRXYKZCzQSq1Km%25lkp@intel.com/

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v2:
  Addresed a minor comment about description (Wei Huang).
v1:
  https://lore.kernel.org/lkml/162947718839.12313.2592762168334394449.stgit@bmoger-ubuntu/

 arch/x86/kernel/cpu/resctrl/monitor.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 57e4bb695ff9..8caf871b796f 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -304,6 +304,12 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
 	case QOS_L3_MBM_LOCAL_EVENT_ID:
 		m = &rr->d->mbm_local[rmid];
 		break;
+	default:
+		/*
+		 * Code would never reach here because an invalid
+		 * event id would fail the __rmid_read.
+		 */
+		return RMID_VAL_ERROR;
 	}
 
 	if (rr->first) {