sdbusplus: use shorter type aliases

The sdbusplus headers provide shortened aliases for many types.
Switch to using them to provide better code clarity and shorter
lines.  Possible replacements are for:
  * bus_t
  * exception_t
  * manager_t
  * match_t
  * message_t
  * object_t
  * slot_t

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If9a7314dade153dd7dbd149a76352aca8257839d
diff --git a/mmc/activation_mmc.hpp b/mmc/activation_mmc.hpp
index 68caf36..aca8811 100644
--- a/mmc/activation_mmc.hpp
+++ b/mmc/activation_mmc.hpp
@@ -22,7 +22,7 @@
     Activations activation(Activations value) override;
 
   private:
-    void unitStateChange(sdbusplus::message::message& msg) override;
+    void unitStateChange(sdbusplus::message_t& msg) override;
     void startActivation() override;
     void finishActivation() override;
 };