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/bus/match.cpp b/test/bus/match.cpp
index ee76972..2d95cf9 100644
--- a/test/bus/match.cpp
+++ b/test/bus/match.cpp
@@ -6,7 +6,7 @@
 class Match : public ::testing::Test
 {
   protected:
-    sdbusplus::bus::bus bus = sdbusplus::bus::new_bus();
+    sdbusplus::bus_t bus = sdbusplus::bus::new_bus();
 
     static constexpr auto busName = "xyz.openbmc_project.sdbusplus.test.Match";