bus: shorten bus type

Create an alias `sdbusplus::bus_t` to `sdbusplus::bus::bus` to reduce
duplication.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I9f17892eed5112d49469498614884c02bba86011
diff --git a/src/server/interface.cpp b/src/server/interface.cpp
index a72c656..166a80c 100644
--- a/src/server/interface.cpp
+++ b/src/server/interface.cpp
@@ -9,7 +9,7 @@
 namespace interface
 {
 
-interface::interface(sdbusplus::bus::bus& bus, const char* path,
+interface::interface(sdbusplus::bus_t& bus, const char* path,
                      const char* interf,
                      const sdbusplus::vtable::vtable_t* vtable, void* context) :
     _bus(bus.get(), bus.getInterface()),