PerformScan: Make registerCallback() static

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I2e6e5bcf35b60049c0f733ac1e78b17e1bfac0bd
diff --git a/src/PerformScan.cpp b/src/PerformScan.cpp
index b6667dc..7caff06 100644
--- a/src/PerformScan.cpp
+++ b/src/PerformScan.cpp
@@ -87,9 +87,9 @@
     }
 }
 
-void registerCallback(nlohmann::json& systemConfiguration,
-                      sdbusplus::asio::object_server& objServer,
-                      const std::string& path)
+static void registerCallback(nlohmann::json& systemConfiguration,
+                             sdbusplus::asio::object_server& objServer,
+                             const std::string& path)
 {
     static boost::container::flat_map<std::string, sdbusplus::bus::match::match>
         dbusMatches;