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: Ibd2a0b512bfb7caf65bfab64b271d194da520aac
diff --git a/app/watchdog_service.hpp b/app/watchdog_service.hpp
index 141bdb7..1a5486a 100644
--- a/app/watchdog_service.hpp
+++ b/app/watchdog_service.hpp
@@ -94,7 +94,7 @@
 
   private:
     /** @brief sdbusplus handle */
-    sdbusplus::bus::bus bus;
+    sdbusplus::bus_t bus;
     /** @brief The name of the mapped host watchdog service */
     static ipmi::ServiceCache wd_service;