Use system include directives for libpldm headers

libpldm is now an external dependency rather than an in-tree library.
Adjust the includes accordingly.

Change-Id: Ib2590b823039d3127d65f66976b294a2fb88e9c1
Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
diff --git a/platform-mc/numeric_sensor.cpp b/platform-mc/numeric_sensor.cpp
index ee4ccdc..a0d5dbb 100644
--- a/platform-mc/numeric_sensor.cpp
+++ b/platform-mc/numeric_sensor.cpp
@@ -1,10 +1,10 @@
 #include "numeric_sensor.hpp"
 
-#include "libpldm/platform.h"
-
 #include "common/utils.hpp"
 #include "requester/handler.hpp"
 
+#include <libpldm/platform.h>
+
 #include <limits>
 #include <regex>