mcerr_monitor: fix CPU numbering in message

The CPU number is intended to be provided as the human-readable number,
so incrementing by one is not correct.

Tested:
Confirmed that the provided CPU number is shown in the message.

Change-Id: I90181720227c914aa010310e6b238bc11acf4481
Signed-off-by: Jason M. Bills <jason.m.bills@intel.com>
diff --git a/include/error_monitors/mcerr_monitor.hpp b/include/error_monitors/mcerr_monitor.hpp
index dfe9fc0..a0d2dce 100644
--- a/include/error_monitors/mcerr_monitor.hpp
+++ b/include/error_monitors/mcerr_monitor.hpp
@@ -30,7 +30,7 @@
 
     void logEvent() override
     {
-        std::string msg = "MCERR on CPU " + std::to_string(cpuNum + 1);
+        std::string msg = "MCERR on CPU " + std::to_string(cpuNum);
 
         sd_journal_send("MESSAGE=HostError: %s", msg.c_str(), "PRIORITY=%i",
                         LOG_INFO, "REDFISH_MESSAGE_ID=%s",