bmc: use latest sdbusplus match APIs

Change-Id: I02aca5f8c7e633c6de7608194a0bdb0874ef2090
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/bmc_state_manager.cpp b/bmc_state_manager.cpp
index 4559c80..9929059 100644
--- a/bmc_state_manager.cpp
+++ b/bmc_state_manager.cpp
@@ -130,23 +130,15 @@
     return;
 }
 
-int BMC::bmcStateChangeSignal(sd_bus_message *msg, void *userData,
-                              sd_bus_error *retError)
-{
-    return static_cast<BMC*>(userData)->bmcStateChange(msg, retError);
-}
-
-int BMC::bmcStateChange(sd_bus_message *msg,
-                        sd_bus_error *retError)
+int BMC::bmcStateChange(sdbusplus::message::message& msg)
 {
     uint32_t newStateID {};
     sdbusplus::message::object_path newStateObjPath;
     std::string newStateUnit{};
     std::string newStateResult{};
 
-    auto sdPlusMsg = sdbusplus::message::message(msg);
     //Read the msg and populate each variable
-    sdPlusMsg.read(newStateID, newStateObjPath, newStateUnit, newStateResult);
+    msg.read(newStateID, newStateObjPath, newStateUnit, newStateResult);
 
     //Caught the signal that indicates the BMC is now BMC_READY
     if((newStateUnit == obmcStandbyTarget) &&