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.cpp b/mmc/activation_mmc.cpp
index b5a5669..a50e99b 100644
--- a/mmc/activation_mmc.cpp
+++ b/mmc/activation_mmc.cpp
@@ -16,7 +16,7 @@
 void ActivationMMC::startActivation()
 {}
 
-void ActivationMMC::unitStateChange(sdbusplus::message::message&)
+void ActivationMMC::unitStateChange(sdbusplus::message_t&)
 {}
 
 void ActivationMMC::finishActivation()