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/test/server/object.cpp b/test/server/object.cpp
index 76e077d..abbb412 100644
--- a/test/server/object.cpp
+++ b/test/server/object.cpp
@@ -16,7 +16,7 @@
 {
   protected:
     sdbusplus::SdBusMock sdbusMock;
-    sdbusplus::bus::bus bus = sdbusplus::get_mocked_new(&sdbusMock);
+    sdbusplus::bus_t bus = sdbusplus::get_mocked_new(&sdbusMock);
 
     static constexpr auto busName = "xyz.openbmc_project.sdbusplus.test.Object";
     static constexpr auto objPath = "/xyz/openbmc_project/sdbusplus/test";