resource messages: make functions inline

clang14 complains about building this header.

Tested: clang14 builds successfully.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: Ib6be59babb0fdc9cc033385b4b71f1c9c88dfa44
diff --git a/redfish-core/include/resource_messages.hpp b/redfish-core/include/resource_messages.hpp
index e66ae6f..0b0773e 100644
--- a/redfish-core/include/resource_messages.hpp
+++ b/redfish-core/include/resource_messages.hpp
@@ -8,7 +8,7 @@
 namespace messages
 {
 
-nlohmann::json
+inline nlohmann::json
     getLogResourceEvent(redfish::registries::resource_event::Index name,
                         std::span<const std::string_view> args)
 {